Lenses for use in the infrared (IR) wavelength region are key elements of IR image sensors, and determine the cost and performance of such sensors. As an alternative to a conventional lens, we designed and fabricated a silicon-based metalens in order to realize a compact, high-performance IR focal plane array (IRFPA) system. The metalens was developed using an automatic inverse design technique based on a rigorous coupled wavelength analysis. It consisted of a periodic array of pillars fabricated by deep reactive-ion etching of a silicon wafer. This metalens was designed for the 80×60 IRFPA used in the Mitsubishi Electric Corporation MIR8060B1, which comprises an array of pn-junction diodes formed on a silicon-on-insulator layer. It is expected that this metalens-based IR sensor will expand the range of applications of such sensors.
Although black phosphorous (BP) is a promising two-dimensional material for next-generation infrared (IR) photodetectors, enhancing its quantum efficiency remains challenging. Herein, we proposed a hybrid BP–plasmonic nanograting with high aspect ratios for use in advanced functional IR photodetectors. Plasmonic nanogratings with high aspect ratios exhibit wide-angle near-unity absorption in the IR-wavelength region; this absorption is based on the grating depth. By forming BP on top of the plasmonic nanogratings and modifying the edge structure of BP, we achieved a hybrid structure that exhibits strong absorption. The results demonstrate the viability of BP-based high-performance IR photodetectors.
Graphene/semiconductor heterojunction photodiodes that use photogating are expected to perform better than conventional infrared (IR) photodetectors. However, interface instability limits has prevented the realization of the theoretically predicted performance and high reliability for these devices. This study focuses on optimizing the material and thickness of an interfacial layer in a graphene/InSb heterojunction to achieve a high-performance mid-IR photodetector. The results indicate that HfO2 is a more suitable material than Al2O3 for the interfacial layer, and 1-2 nm is the thickness that best promotes effective photocurrent transport. This interfacial layer can facilitate the fabrication of superior IR image sensors based on graphene/InSb heterojunctions.
Graphene-based infrared photodetectors are promising devices that exploit the unique optoelectronic properties of graphene, including its broadband light absorption characteristics, rapid response, and high chemical stability. However, graphene exhibits a low absorbance (2.3%), which limits its photoresponsivity. This paper introduces sensitivity-enhanced InAs/GaInSb type-II superlattice (T2SL) infrared photodetectors fabricated using a graphene diode structure. The devices consist of graphene diodes and InAs/GaInSb SLs grown via chemical vapor deposition. The T2SL structure is employed for both photocarrier supply source and carrier density modulation of the graphene diodes to improve the sensitivity of the devices. The dark current in the graphene diode device is reduced to less than 1%, which is lower than that in the GFET device, and the responsivity of the devices is significantly enhanced using the photogating effect. These highly sensitive and low-dark-current devices are expected to promote the development of high-performance graphene-based image sensors.
Multispectral uncooled infrared (IR) sensors are attracting interest for use in applications such as gas analysis, hazardous material recognition, and biological analysis. However, conventional sensors require additional filters or a resonant structure in the vertical direction. To address this challenge, we investigated plasmonic metamaterial absorbers (PMAs) such as plasmonic crystals (PCs), metal–insulator–metal (MIM), and mushroom-type PMAs. Such PMAs exhibit wavelength-selective absorption by surface plasmon resonance (SPR, and the absorption wavelength can be controlled by modifying the features of the surface pattern (e.g., the periodicity of dimples and the micropatch size). Previously, we fabricated thermopiles with PC-type PMAs and used them for wavelength-selective detection. Although PC-type PMAs have advantages such as easy fabrication, robustness against structural fluctuations, and a wide operating wavelength range, they suffer from an incidence-angle dependence and require a large absorber volume. Here, we fabricated thermopiles with encapsulated MIM (EMIM)-type PMAs using a complementary metal oxide semiconductor process. The devices consist of a top encapsulated layer, periodic top micropatches, a flat insulator layer, and a bottom reflector. The encapsulated layer functions as a protective layer. Like MIM-type PMAs, the EMIM-type PMAs exhibit incidence-angle independence and a thin absorber volume, where the top micropatch induces localized SPR with the bottom reflector, and its size mainly determines the absorption wavelength. Spectral measurements showed that wavelength-selective IR detection can be performed in the mid-IR wavelength range without any additional filters. We expect the obtained results to contribute to the realization of advanced functional uncooled IR sensors and expand their range of applications.
Graphene/InSb heterojunction mid-infrared photodiodes for infrared image sensors exhibit high responsivity, low noise, and excellent detection performance. However, the performance of each pixel varies owing to the instability of the graphene/InSb interface state. In this study, the performance variation was addressed by inserting an interfacial layer at the graphene/InSb interface. A few-nanometer-thick HfO2 interfacial layer was inserted at the graphene/InSb interface. Compared to devices without an interfacial layer, those with an interfacial layer exhibited greatly improved minimum noise equivalent temperature difference (NETD) and pixel-by-pixel NETD variation. This was due to the stabilization of the InSb surface and increased photocurrent caused by photoswitching, which significantly changed the Fermi level of the graphene. The insertion of the HfO2 interfacial layer improved the standard deviation to less than 1/30. Thus, inserting an interfacial layer at the graphene/InSb interface is expected to facilitate the development of high-performance infrared image sensors with low variability.
Graphene infrared (IR) photodetectors are promising devices that exploit the unique optoelectronic properties of graphene, such as broadband light absorption, rapid response, and high-chemical stability. However, graphene has low absorbance (2.3%), which limits its photo-responsivity. This study investigated the middle-wavelength infrared (MWIR) and long-wavelength IR (LWIR) responsivity enhancements in graphene photodetectors with type-II superlattices (T2SL) employed as photosensitizers. Graphene field-effect transistors (GFETs) were fabricated with the InAs/InGaSb SL photosensitizers on a GaSb substrate. The device was vacuum-cooled and then exposed to light using a filament lamp (wavelength ranges: 3–5 μm and 8–12 μm). The device exhibited MWIR and LWIR photoresponses at 77 K, whereas no photoresponse was observed when photosensitizers were not used. The observed current variations in the photosensitizers and the substrate suggest that photocarriers in the InAs/InGaSb SL modulate the gate voltages on the GFETs, thereby producing the photogating effect. The LWIR photoresponse in conjunction with the photogating effect was enhanced by a factor of 1500 compared with that without the photosensitizers. The results obtained in this study are expected to contribute to the development of high-performance graphene-based IR image sensors.
Black phosphorous (BP) is a promising material for infrared (IR) photodetectors. We theoretically investigated and proposed BP/graphene van der Waals (vdW) heterostructure-based metasurface wavelength-selective IR photodetectors that operate on the basis of plasmonic resonance. The proposed structure consists of a top layer consisting of periodic monolayers of BP, a graphene-based vdW heterostructure layer on a middle dielectric layer, and a bottom reflector. The periodic BP produces polarization-dependent localized surface plasmon resonance (LSPR) according to its armchair or zigzag edge, resulting in strong wavelength-selective absorption. The graphene layer can enhance the LSPR of BP, inducing propagating surface plasmon resonance on graphene. These results will contribute to the realization high-performance BP/graphene-based IR photodetectors.
Graphene nanoribbons (GNRs) and graphene hybrid photodetectors were demonstrated in the middle- and long-wavelength infrared (MWIR and LWIR, respectively) regions. Graphene transistors were prepared using Si substrates with an SiO2 layer and source and drain electrodes. Single-layer graphene fabricated by chemical vapor deposition was transferred onto the substrates to form a channel; the GNR was formed on this channel by solution dispersion. The formation of graphene and the GNR was confirmed by position mapping of the Raman spectra. The photoresponse was measured in the MWIR and LWIR regions, and was found to be drastically enhanced for devices with the GNR when compared with those without it. Although the devices without the GNR could not respond at temperatures higher than 15 K, those with the GNR could be operated at temperatures up to 150 K. This was attributed to photogating by the GNR layers that absorbed the MWIR and LWIR radiation, leading to a significant temperature change. These results can potentially contribute toward developing high-performance and broadband IR graphene-based photodetectors.
Herein, we developed a high-performance graphene/InSb heterojunction mid-infrared (IR) photogated diode for IR image sensors. We achieved low noise owing to a significant reduction in the dark current and high responsivity, which is attributed to the graphene/InSb heterojunction diode structure and the photogating effect. The detection performance of the proposed device is better than that of conventional graphene-based IR sensors in the mid-infrared region of 3–5 μm. These results indicate that the combination of a simple graphene/InSb heterojunction and the photogating effect can produce IR image sensors with better detection performance than existing IR sensors.
In this study, room-temperature long-wavelength infrared (LWIR) graphene photodetectors using pyroelectric photosensitizers are demonstrated. The devices comprise graphene-based field-effect transistors with lithium niobate as a pyroelectric photosensitizer. To enhance the photodetector performance, we studied the influence of photosensitizer thickness and ferroelectric polarization direction on the pyroelectric photogating effect. Modulation of the gate current indicates that the IR photoresponse is considerably amplified by thick photosensitizers in which dielectric polarization occurs in the direction perpendicular to the graphene channel. The results will contribute to the development of high-performance graphene LWIR image sensors.
We theoretically propose van der Waals (vdW) heterostructure-based wavelength selective infrared (IR) photodetectors using plasmonic metasurfaces (PMs), consisting of top micropatches, graphene on a hexagonal boron nitride (hBN) vdW heterostructure layer, and a bottom reflector. The hBN ensures the vdW heterostructures maintain high carrier mobility in the graphene. The wavelength selective detection of the graphene can be controlled mainly by the micropatch size over a wide range from the middle- to long-wavelength IR regions. The wavelength can also be electrically tuned by the chemical potential of the graphene. These results will contribute to developing high-performance wavelength tunable graphene/hBN-based IR photodetectors.
Graphene, an atomically thin carbon sheet with a two-dimensional hexagonal lattice structure, has attracted attention because of its unique electronic and optical properties. Graphene has two promising optical applications: graphene photodetectors that can operate at various wavelengths, and resistive graphene sheets whose optical constants can be configured via an applied voltage. In particular, graphene is a candidate for plasmonic metamaterial absorbers and emitters because of its electrical tunability. We previously demonstrated the concept of multilayer graphene-based metasurfaces. In the present study, we developed a more accurate theoretical calculation model for graphene, and theoretically investigated graphene nanoribbon metasurface absorbers (GNRMAs) for single- or multi-band infrared detection. The GNRMAs consist of a top periodic graphene nanoribbon layer formed on a dielectric layer, which contains another periodic graphene nanoribbon layer and is formed on a back-reflector. High wavelength-selective absorption can be achieved because of the surface plasmon resonance (SPR) of the graphene nanoribbons and Fabry– Pérot resonance of the dielectric layer. The wavelength of graphene SPR is determined mainly by the width of the graphene nanoribbon. The absorption wavelength can be electrically tuned via the chemical potential of graphene, which can be controlled by the voltage applied to the graphene nanoribbons. The gap between the graphene nanoribbon layers determines whether the absorption is single-band or multi-band. This electrical tunability can be enhanced by independently controlling the voltage applied to each graphene nanoribbon layer. These results will contribute to the development of electrically tunable graphene-based multispectral infrared detectors and emitters.
Graphene is a promising material for various optical and electrical device applications because of its high carrier mobility, broadband photoresponse, and low manufacturing cost. One such application is for infrared (IR) photodetectors (PDs) because conventional quantum-type IR PDs require complex and toxic materials such as HgCdTe and Type II superlattice structures. We have developed high-performance graphene IR PDs, which operate in the middle-wavelength or long-wavelength IR (MWIR or LWIR) regions, based on field-effect transistors (FETs) that use a photogating effect. This effect is induced by photosensitizers located around the graphene to produce a voltage change under incident light, inducing a change in the electric current of the graphene, which is attributed to its high carrier mobility and single-atom thickness. Si, InSb, and LiNbO3 were used as the photosensitizers for the visible to near-IR, MWIR, and LWIR, respectively. The photoresponsivity obtained for each wavelength region was more than 10 times greater than that of conventional PDs. However, graphene FET-based structures inevitably produce a large dark current and require three electrical ports, which significantly degenerates the PD performance, inhibiting the use of readout integrated circuits for the IR image sensors. To address this issue, we have developed graphene photogated diodes (GPDs) with graphene/semiconductor heterojunction structures. The GPDs employ Schottky barrier lowering and carrier density modulation by photogating and have recently realized low dark currents and high responsivities because of the graphene/semiconductor Schottky junction and photogating. These results can contribute to the development of high-performance graphene-based IR image sensors.
Graphene—atomically thin carbon sheets with a two-dimensional hexagonal lattice structure—exhibits unusual electronic and optical properties. Photodetectors are a good prospective application of graphene because they should ideally exhibit a broadband photoresponse from the ultraviolet to terahertz regions and high-speed operation, as well as be inexpensive to produce. Numerous methods have been proposed in order to enhance the responsivity of graphene-based photodetectors. Among these methods, photogating is most promising because it can realize the highest performance. Photogating requires photosensitive layers at the vicinity of graphene in order to produce a voltage change. Various photosensitive layers, including quantum dots, Si, InSb, and LiNbO3, are used in the visible to near-, mid-, and long-wavelength IR (NIR, MWIR, and LWIR) regions, respectively. However, the operating wavelength region is determined by the photosensitive layer, which undermines the advantage of broadband operation of the graphene. In this work, graphene nanoribbon (GNR) was used as a photosensitive layer. Graphene transistors were prepared using Si substrates with a SiO2 layer and source and drain electrodes. Single-layer graphene fabricated by chemical vapor deposition was transferred onto this substrate and formed a channel, and GNR was formed on the graphene channel using a solution dispersion method. The photoresponse was measured in the mid- and long-wavelength infrared regions. The photoresponse was found to be enhanced by GNR photogating compared with the photoresponse of devices without GNR. These results are expected to contribute to the development of high-performance broadband IR photodetectors.
There is a growing interest in low-cost small-format infrared array sensors. In this study, we demonstrate the properties of small-format graphene infrared array sensors. The devices consisted of 9 x 9 pixels, which were composed of graphene field-effect transistors (FETs) and graphene/semiconductor Schottky barrier diodes (SBDs). The photoresponses of these devices were evaluated under middle-wavelength infrared (MWIR) light irradiation. The graphene FETs exhibited ultrahigh responsivity owing to modulation of the field-effect and surface carriers caused by photocarriers generated in photosensitizers. The MWIR photoresponse of the graphene FETs was enhanced by photogating. Compared to the FETs, the SBDs showed improved dark current characteristics. The photocarriers injected into the graphene were amplified by the photogating effect induced in the graphene/insulator region. Line-scan MWIR images and profiles were obtained; the devices were mounted in ceramic image sensor packages and vacuum-cooled. They were then exposed to a scanning blackbody light source, and the MWIR photoresponse was evaluated. The photocurrent linearly increased with the step shift of the blackbody source. The results obtained in this study will contribute to the development of high-performance graphene-based IR image sensors.
This study investigated the fabrication and performance of highly responsive photodetectors, constructed of turbostratic stacked graphene produced via chemical vapor deposition (CVD) and using the photogating effect. This effect was induced by situating photosensitizers around a graphene channel such that these materials coupled with incident light and generated large electrical changes. The responsivity of such devices correlates with the carrier mobility of the graphene, and so improved mobility is critical. This work assessed the feasibility of using turbostratic stacked CVD graphene to improve mobility since, theoretically, multilayers of this material may exhibit linear band dispersion, similar to monolayer graphene. This form of graphene also exhibits higher carrier mobility and greater conductivity than monolayer CVD graphene. The turbostratic stacking can be accomplished simply by the repeated transfer of graphene monolayers produced by CVD. Furthermore, it is relatively easy to fabricate CVD graphene layers having sizes suitable for the mass production of electronic devices. Unwanted carrier scattering that can be caused by the substrate is also suppressed by the lower graphene layers when turbostratic stacked graphene is applied. The infrared response properties of the multilayer devices fabricated in the present work were found to be approximately tripled compared with those of a monolayer graphene photodetector. It is evident that turbostratic stacked CVD graphene, which can be produced on a large scale, serves to increase the responsivity of photodetectors in which it is included. The results of this study are expected to contribute to the realization of low-cost, mass-producible, high-responsivity, graphene-based infrared sensors.
Infrared (IR) rectification is promising for high-performance IR detection at room temperature. We propose metal– insulator–metal (MIM)-based plasmonic structures incorporating a nanoslit for IR rectification. Gold and SiO2 were used as the metal and insulator layers, respectively. A high-aspect-ratio nanoslit was incorporated onto the top of the metal layer of an MIM structure. This slit works as a coupler for incident IR light, and a surface plasmon mode is induced in the slit. The coupled IR light is then guided into the middle insulator layer and waveguide modes are formed. Rectification can be achieved by applying a voltage between the top and bottom metal layers. Finite-difference timedomain calculations show that wavelength selective detection can be achieved by controlling the slit width or depth. However, these proposed structures are difficult to fabricate because a metal-based high-aspect-ratio nanoslit cannot be formed by conventional dry or wet etching. We have developed fabrication procedures using gold electroplating and chemical mechanical polishing (CMP). The former method uses a photoresist as a sacrificial layer for the narrow slit, and the top metal is formed by electroplating. The latter uses SiO2 as a sacrificial layer, and the top metal is formed by sputtering and CMP. Both methods can be used to fabricate an MIM structure with a nanoslit. It was found that the CMP method can achieve a higher aspect ratio. These proposed structures and fabrication techniques could contribute to the development of novel IR detectors using plasmonic rectification.
Graphene is a promising material for next-generation high-performance photodetectors because of its fast response, broadband photodetection (from the ultraviolet region to the terahertz region), mechanical and chemical stability, flexibility, and low manufacturing cost. We developed high-responsivity graphene infrared (IR) photodetectors based on field-effect transistors (FETs) with photogating that operate in the middle- or long-wavelength IR (MWIR or LWIR) region. The photogating effect is induced by a photosensitizer located in the vicinity of graphene. The photosensitizer generates a voltage change via incident light, which modulates the carrier density of graphene and produces an extremely large differential output current. This effect, unique to graphene, is attributed to its high carrier mobility and single-atom thickness. As photosensitizers, InSb and LiNO3 were used for the MWIR and LWIR regions, respectively. However, graphene FET-based structures inevitably produce a large dark current because graphene has no bandgap. This degenerates photodetector performance and prevents the construction of IR image sensors using conventional readout integrated circuits. To overcome this problem, a graphene/InSb heterostructure is proposed. It exhibits both a low dark current and a high responsivity by amplifying injected photocarriers via photogating in the MWIR region. These results can be applied to other wavelength regions and could contribute to the development of high-performance graphene-based IR image sensors and next-generation optoelectronic devices.
The photoresponse mechanism of graphene/InSb heterojunction middle-wavelength infrared (MWIR) photodetectors was investigated. The devices comprised a graphene/InSb heterojunction as a carrier-injection region and an insulator region of graphene on tetraethyl orthosilicate (TEOS) for photogating. The MWIR photoresponse was significantly amplified with an increase in the graphene/TEOS cross-sectional area by covering the entire detector with graphene. The graphene-channel dependence of the MWIR photoresponse indicated that the graphene carrier density was modulated by photocarrier accumulation at the TEOS/InSb boundary, resulting in photogating. The dark current of the devices was suppressed by a decrease in the graphene/InSb carrier-injection region and the formation of the heterojunction using an n-type InSb substrate. The results indicate that photocarrier transportation was dominated by the formation of a Schottky barrier at the interface of the graphene/InSb heterojunction and a Fermi-level shift under bias application. The high-responsivity and low-dark-current photoresponse mechanism was attributed to the graphene/InSb heterojunction diode behavior and the photogating effect. The devices combining the aforementioned features had a noise equivalent power of 0.43 pW / Hz1/2. The results obtained in our study will contribute to the development of high-performance graphene-based IR image sensors.
Graphene, an atomically thin carbon sheet, has drawn significant attention in many fields because of its unique electronic and optical properties. Graphene is a potential candidate for plasmonic metamaterial absorbers and emitters because of its optical tunability and extreme thinness. We have previously demonstrated graphene Salisbury screen metasurfaces. Although the absorption wavelength of such metasurfaces can be controlled by varying the graphene patch size, the absorbance is insufficient for practical applications. In this study, therefore, multilayer graphene metamaterial absorbers (MGMAs) were theoretically investigated in the middle- to long-wavelength infrared (IR) region. The MGMAs consist of graphene layers alternating with insulator layers formed on a bottom reflector. The spectral absorbance was calculated using the rigorous coupled-wave analysis method. The calculation results demonstrated that a high absorption of ~100% can be achieved because of the multiple plasmonic resonance between each graphene layer and the bottom reflector. The absorption wavelength can be controlled by regulating the graphene pattern size because of the plasmonic resonance of graphene. Furthermore, the absorption wavelength can be tuned by controlling the chemical potential of graphene, which allows for the development of electrically tunable wavelength-selective IR absorbers and emitters. These results will contribute to the development of high-performance wavelength-tunable graphene-based IR detectors and emitters.
Graphene has unique optoelectronic properties and potential applications in improved infrared (IR) photodetectors. Due to its Dirac cone structure, graphene exhibits broadband light absorption and rapid responsivity. In addition, unlike conventional quantum photomaterials, graphene can be synthesized inexpensively via a non-toxic process. Although graphene has advantages in IR photodetector applications, graphene photodetectors have shown low responsivity due to their minimal IR absorption (just 2.3%) and also require cooling. Therefore, there is considerable interest in enhancing the responsivity of graphene photodetectors operating at room temperature so that their advantages can be employed in IR applications. The present work demonstrates room temperature, high-responsivity, long-wavelength infrared (LWIR) graphene photodetectors. These devices operate on the photogating effect, using a lithium niobate (LiNbO3) substrate with enhancement of the photogating via a pyroelectric effect in the substrate in conjunction with a SiN layer. This effect significantly modulates the back-gate voltage to increase the photoresponse by a factor of approximately 600 compared to that for a conventional graphene photodetector. This work also found a change in the type of charge carrier with variations in temperature, which was attributed to a large shift in the Dirac point owing to the strong photogating effect. The results of this study are expected to contribute to the future realization of high-responsivity, low-cost LWIR photodetectors for applications such as thermal imaging, medical care and gas analysis.
Disorderly stacked multilayer graphene, called turbostratic graphene, is a promising candidate for highly responsive infrared detectors due to its higher carrier mobility than well-ordered multilayer graphene, and facility to suppress the Coulomb scattering from the substrate. Such properties are expected to enhance photogating for high-responsivity infrared detection. The electronic structure of turbostratic graphene was investigated using first-principles calculations. The turbostratic graphene was modeled by introducing disorder to bilayer graphene in terms of the distance and the rotation angle between the graphene layers. The calculation results show that an increase in these parameters leads to linear band dispersion and a structure similar to monolayer graphene.
Graphene infrared (IR) photodetectors are promising devices that take advantage of the unique optoelectronic properties of graphene, such as broadband light absorption, rapid response, and high chemical stability. Despite its advantages, graphene has a low absorbance of 2.3%, which limits its photoresponsivity. We have previously reported the responsivity enhancement of graphene middle wavelength IR (MWIR) photodetectors using the photogating effect. The photogating effect is induced by photosensitizers located around the graphene channel that generate a large electrical change. The MWIR photoresponse with the photogating effect was enhanced by 100-fold relative to conventional graphene field-effect transistors (FETs). Although our graphene FETs using photogating exhibited ultrahigh responsivity, the dark current was extremely high, as in the case of conventional graphene FETs, because the normally-OFF operation cannot be realized in graphene. Therefore, reducing the high dark current is essential for applying graphene photodetectors to IR applications. We demonstrate dark current reduction and high responsivity MWIR light detection in graphene MWIR photodetectors. The devices consist of graphene FETs with a carrier injection region. The dark current is reduced by applying a bias voltage. The photocarriers injected into the graphene are amplified by the photogating effect induced in the graphene/insulator region. The dark current of the devices was significantly suppressed compared with that of conventional graphene FETs. The photoresponse characteristics were investigated for devices of different structure sizes. The results obtained in this study will contribute to the development of high-performance graphene-based IR image sensors.
Advanced uncooled infrared (IR) sensors with wavelength- or polarization-selectivity are advantageous in applications such as fire detection, gas analysis, hazardous material recognition, biological analysis, and polarimetric imaging. Plasmonic metasurfaces (PM) are potential candidates to realize such functionality over a wide range of wavelength, i.e., middle- to long-wavelength IR regions. In particular, metal-insulator-metal (MIM) PMs are most suitable for image sensor applications because of their small pixel size and simple surface configuration. However, such PMs produce various absorption modes, of which some degrade the wavelength or polarization selectivity. In this study, therefore, control of the absorption modes of PMs was investigated for wavelength- or polarization-selective uncooled IR sensor applications. The PMs produce various absorption modes, namely, localized surface plasmon resonance (LSPR), waveguide, Fabry-Pérot, and plasmonic surface lattice resonance (PSLR) modes. These modes can be controlled by engineering the surface configuration or optimizing the dielectric material. The LSPR mode is appropriate for wide-angle detection because it does not depend on the incident angle, whereas the PSLR mode is a potential candidate for narrowband uncooled IR sensors. The waveguide mode, which can degrade the wavelength and polarization selectivity, can be eliminated using an appropriate dielectric material, such as SiO2 or SiN, for high-performance wavelength- or polarization-selective uncooled IR sensors.
We demonstrated a middle-wavelength infrared (MWIR) graphene photodetector using the photogating effect. This effect was induced by photosensitizers situated around a graphene channel that coupled incident light and generated a large electrical charge. The graphene-based MWIR photodetector consisted of a top graphene channel, source–drain electrodes, an insulator layer, and a photosensitizer, and its photoresponse characteristics were determined by current measurements. Irradiation of the graphene channel of the vacuum cooled device by an MWIR laser generated a clear photoresponse, as evidenced by modulation of the output current during irradiation. The MWIR photoresponse with the photogating effect was 100 times greater than that obtained from conventional graphene photodetectors without the photogating effect. The device maintained its MWIR photoresponse at temperatures up to 150 K. The effect of the graphene channel size on the responsivity was evaluated to assess the feasibility of reducing the photodetector area, and decreasing the channel area from 100 to 25 μm2 improved the responsivity from 61.7 to 321.0 AW − 1. The results obtained in our study will contribute to the development of high-performance graphene-based IR imaging sensors.
Graphene-based transistors were investigated as simple photodetectors for a broad range of wavelengths. Graphene transistors were prepared using p-doped silicon (Si) substrates with a SiO2 layer, and source and drain electrodes. Monolayer graphene was fabricated by chemical vapor deposition and transferred onto the substrates, and the graphene channel region was then formed. The photoresponse was measured in the broadband wavelength range from the visible, near-infrared (NIR), and mid- to long-wavelength IR (MWIR to LWIR) regions. The photoresponse was enhanced by the photogating induced by the Si substrate at visible wavelengths. Enhancement by the thermal effect of the insulator layer became dominant in the LWIR region, which indicates that the photoresponse of graphene-based transistors can be controlled by the surrounding materials, depending on the operation wavelength. These results are expected to contribute to provide the key mechanism of high-performance graphene-based photodetectors.
Wavelength-selective uncooled infrared (IR) sensors have significant advantages for applications such as fire detection, gas analysis, hazardous material recognition, and biological analysis. We have demonstrated a wavelength-selective uncooled IR sensor with a plasmonic metamaterial absorber (PMA). However, unwanted modes are a serious issue for wavelength-selective detection and are attributed to the absorption by the materials used in the sensors that do not consist of PMAs. Elimination of unwanted modes in a wavelength-selective uncooled IR sensor with a PMA is demonstrated using a subtraction operation with a reference pixel. The reference pixel has the same sensor structure, except for the absorber area; a flat mirror was instead formed on the absorber surface. Wavelength-selective uncooled IR sensors were fabricated with PMAs and the reference pixels. Single-mode detection was achieved by the subtraction operation with the reference pixel.
Advanced functional infrared (IR) photodetectors with wavelength selectivity are promising for a wide range of applications, such as multicolor imaging, gas analysis and biomedical analysis. Graphene is considered to be a promising material for novel IR detectors. However, the absorption of graphene is constant at approximately 2.3% and rather small. We have developed multispectral high-performance graphene IR photodetectors using metal-insulator-metal (MIM) or single-layer (SL) plasmonic metasurfaces (PMs). MIM- or SL-PMs induce localized surface plasmons on their surfaces and enhance absorption at the wavelength, which can be controlled by their surface patterns, such as the period or the gaps between micropatches. The absorption of graphene with PMs was theoretically investigated for various structural parameters. The absorption wavelength can be controlled based on plasmonic resonance by varying the surface geometry of the PMs. Graphene-based IR photodetectors with SL-PMs were fabricated by the chemical vapor deposition of graphene and then transferred onto the PMs. Wavelength-selective enhancement of the optical absorption and detection by graphene could be achieved due to the effect of the PMs. The results obtained here are expected to contribute to the realization of multispectral graphene infrared image sensors.
Graphene has remarkable optoelectronic properties and thus would represent a means to improve infrared (IR) photodetectors. As a result of its Dirac-cone structure, graphene exhibits broadband light absorption and a rapid response. Unlike quantum photomaterials, graphene can also be synthesized inexpensively via a non-toxic process. Despite these advantages, graphene-based photodetectors suffer from low responsivity due to the low absorption of graphene of around 2.3%. Therefore, there is a strong demand to enhance the IR responsivity of graphene photodetectors and expand the range of IR applications. In this study, enhancement of the middle-wavelength IR (MWIR) photoresponsivity of graphene photodetectors using the photogating effect was investigated. The photo-gating effect is induced by photosensitizers, which are located around the graphene channel and couple incident light and generate a large electrical change. The graphenebased MWIR photodetectors consisted of a top graphene channel, source-drain electrodes, insulator layer, and photosensitizer. The photoresponse characteristics were investigated through current measurements using a device analyzer. The device was vacuum-cooled and the graphene channel was irradiated with light from a MWIR laser. The device exhibited a clear MWIR photoresponse observed as modulation of the output current during irradiation. The MWIR photoresponse with the photo-gating effect was 100 times higher than that of conventional graphene photodetectors without the photo-gating effect. The device maintained its MWIR photoresponse at temperatures up to 150 K. The results obtained in this study will contribute to the development of high-performance graphene-based IR image sensors.
Graphene is an atomically thin carbon sheet with a two-dimensional hexagonal lattice structure that has drawn significant attention in many fields due to its unique electronic and optical properties. In this study, graphene Salisbury screen metasurfaces (GSMs) were theoretically investigated as wavelength-selective plasmonic metamaterial absorbers. The GSMs consist of a top graphene sheet, a middle insulator layer and a bottom reflector. The absorption wavelengths of GSMs with a continuous graphene sheet are demonstrated to be controllable according to the insulator layer thickness, which is similar to the case for a conventional Salisbury screen. The insulator thickness can be used to control the optical impedance to incident light using the graphene as a resistive sheet. GSMs with a periodic micropatch array of graphene can be used to control the absorption wavelength, mainly based on the graphene micropatch size and symmetry in conjunction with the insulator thickness. This wavelength selectivity is mainly attributed to the plasmonic resonance in graphene. In both structures, the chemical potential of graphene can be used to tune the absorbance and the absorption wavelength. These results will contribute to the development of electrically tunable and high-performance graphenebased wavelength- or polarization-selective absorbers or emitters.
Graphene, which is carbon arranged in atomically thin sheets, has drawn significant attention in many fields due to its unique electronic and optical properties. Photodetectors are particularly strong candidates for graphene applications due to the need for a broadband photoresponse from the ultraviolet to terahertz regions, high-speed operation, and low fabrication costs, which have not been achieved with the present technology. Here, graphene-based transistors were investigated as simple photodetectors for a broad range of wavelength. The photoresponse mechanism was determined to be dependent on factors such as the operation wavelength, the components near the graphene channel of the photodetector, and temperature. Here, we report the detailed mechanism that defines the photoresponse of graphene-based transistors. Graphene transistors were prepared using doped silicon (Si) substrates with a SiO2 layer, and source and drain electrodes. Single-layer graphene was fabricated by chemical vapor deposition, transferred onto the substrates, and the graphene channel region was then formed. The photoresponse was measured in the visible, near-infrared (NIR), and mid- and long-wavelength IR (MWIR and LWIR) regions. The results indicated that the photoresponse was enhanced by the Si substrate gating at visible wavelengths. Cooling was required at wavelengths longer than NIR due to thermal noise. Enhancement by the thermal effect of the insulator layer becomes dominant in the LWIR region, which indicates that the photoresponse of graphene-based transistors can be controlled by the surrounding materials, depending on the operation wavelength. These results are expected to contribute to the development of high-performance graphenebased photodetectors.
Infrared (IR) polarimetric imaging is drawing significant interest because of its role in the enhancement of object recognition or detection ability. Conventional IR polarimetric imaging requires the use of polarizers or filters with IR cameras, which increases the complexity and cost of such systems, and degenerates performance. If uncooled IR sensors could selectively detect polarization without the need for polarizers or filters, then this would widen their range of applications. We have therefore investigated polarization-selective absorbers based on plasmonic metamaterials. Onedimensional (1D) plasmonic nano-metagrating absorbers (PNMAs) with high aspect ratios (<10) and narrow grooves (ca. 150 nm) are highly promising candidates for this purpose. Numerical calculations indicate that polarization selective absorption of over 90% absorbance is achieved. The incident electromagnetic wave is strongly confined in the narrow grooves and produces plasmonic resonance; the absorption wavelength is defined only by the groove depth and is independent of the incidence angle. Such high aspect ratio gratings with narrow grooves exhibit the optical properties of metamaterials rather than those of conventional metal gratings. We recently developed a top-down fabrication procedure for PNMAs using tapered-sidewall molds with Au deposition, which achieved 100 nm width grooves and an aspect ratio of 15. The absorption wavelengths obtained were larger than the period of the PNMA, and absorption over 90% was achieved. The absorption bandwidth can be controlled according to the groove shape, so narrow and broadband operation can be realized. PNMAs are therefore promising for uncooled IR polarimetric image sensors in terms of both sensor performance and mass production.
Graphene is an atomically thin carbon layer with a two-dimensional hexagonal lattice structure and has rich optoelectronic properties well suited to a wide range of applications. Graphene is considered to be a promising material for photodetectors because it exhibits excellent properties such as broadband absorption covering at least the ultraviolet to terahertz frequencies. However, the low optical absorption of graphene, at ca. 2.3%, still remains an important problem. Plasmonic metamaterial structures are good candidates to address this challenge. Metal-insulator-metal-based plasmonic metamaterial absorbers (MIM-PMAs) are highly suitable for the introduction and application of graphene. MIM-PMAs have a multilayer structure that includes plasmonic micropatches, an insulator, and a metal reflector layer. MIM-PMAs exhibit wavelength-selective absorption according to the micropatch size. Our previous research has demonstrated that the optical absorption of graphene is enhanced only by the main plasmonic resonance mode, and the plasmonic resonance modes in MIM-MPAs are strongly influenced by the insulator material. Therefore, the insulator layer plays an important role in graphene-coated MIM-PMAs. In this study, we have investigated the effect of the insulator layer in graphene-covered MIM-PMAs. The graphene was fabricated by chemical vapor deposition and transferred onto MIM-PMAs with different insulator thicknesses. Reflectance measurements demonstrated that varying the insulator thickness had a significant effect on the absorbance of graphene and resulted in modulation of the absorption wavelength. These results indicate that the plasmonic resonance localized at graphene near the plasmonic micropatches is modulated by the waveguide mode in the insulator layer. We believe that the present study will lead to significant improvements in graphene-based infrared detectors.
Infrared (IR) polarimetric imaging is a promising approach to enhance object recognition with conventional IR imaging for applications such as artificial object recognition from the natural environment and facial recognition. However, typical infrared polarimetric imaging requires the attachment of polarizers to an IR camera or sensor, which leads to high cost and lower performance caused by their own IR radiation. We have developed asymmetric mushroom plasmonic metamaterial absorbers (A-MPMAs) to address this challenge. The A-MPMAs have an all-Al construction that consists of micropatches and a reflector layer connected with hollow rectangular posts. The asymmetric-shaped micropatches lead to strong polarization-selective IR absorption due to localized surface plasmon resonance at the micropatches. The operating wavelength region can be controlled mainly by the micropatch and the hollow rectangular post size. AMPMAs are complicated three-dimensional structures, the fabrication of which is challenging. Hollow rectangular post structures are introduced to enable simple fabrication using conventional surface micromachining techniques, such as sacrificial layer etching, with no degradation of the optical properties. The A-MPMAs have a smaller thermal mass than metal-insulator-metal based metamaterials and no influence of the strong non-linear dispersion relation of the insulator materials constant, which produces a gap in the wavelength region and additional absorption insensitive to polarization. A-MPMAs are therefore promising candidates for uncooled IR polarimetric image sensors in terms of both their optical properties and ease of fabrication. The results presented here are expected to contribute to the development of highperformance polarimetric uncooled IR image sensors that do not require polarizers.
The spectral discrimination function of uncooled infrared (IR) sensors has significant advantages for applications such as fire detection, gas analysis, and biological analysis. We have previously demonstrated wavelength-selective uncooled IR sensors using two-dimensional plasmonic absorbers (2-D PLAs) over a wide range spanning the middle- and long-wavelength IR regions. 2-D PLAs are highly promising in terms of practical application due to the ease of fabrication and robustness for structural fluctuations. However, dual-band operation based on this concept has not yet been investigated, even though the ability to absorb in two different wavelength bands is extremely important for object recognition. Thus, a dual-band uncooled IR sensor was developed that employs Fano resonance in the plasmonic structures. To achieve dual-band detection, asymmetric periods in the orthogonal x- and y-directions were introduced into 2-D PLAs. Theoretical investigations predicted an asymmetric absorbance line shape dependent on the polarization attributed to Fano resonance. The spectral responsivity of the developed sensor demonstrated that selective detection occurred in two different wavelength bands due to polarization-dependent Fano resonance. The results obtained in this study will be applicable to the development of advanced sensors capable of multiband detection in the IR region.
Wavelength-selective uncooled infrared (IR) sensors have significant advantages with regard to applications such as fire
detection, gas analysis, hazardous materials recognition, and biological analysis. We have previously demonstrated an
uncooled IR sensor based on a two-dimensional plasmonic absorber (2D PLA) that exhibited wavelength-selective
absorption over a wide range spanning the middle and long-wavelength IR regions. This device had a Au-based 2D
periodic dimple-array structure, in which surface plasmon modes were induced, leading to wavelength-selective
absorption, such that the absorption wavelength was determined by the period of the surface dimples. However, dual-band
operation based on this concept has not yet been investigated, even though the ability to absorb in two different
wavelength bands is extremely important for object recognition. In the present study, a dual-band uncooled IR sensor
was developed using a 2D PLA with asymmetric dimple periods (2-D PLA-AP). To achieve multiband absorption, the
Au-based dimples in this device were fabricated so as to have different periods in the orthogonal x and y directions.
Theoretical calculations predicted asymmetric absorption spectra, attributed to Fano resonance in the 2-D PLA-AP. A
sensor was subsequently fabricated using complementary metal oxide semiconductor and micromachining techniques.
Measurement of the spectral responsivity demonstrated that selective absorption occurred in two different wavelength
bands, determined by the dimple periods in the x and y directions. The results obtained in this study will be applicable to
the development of advanced sensors capable of multiband detection in the IR region.
Graphene consists of a single layer of carbon atoms with a two-dimensional hexagonal lattice structure. Recently, it has
been the subject of increasing interest due to its excellent optoelectronic properties and interesting physics. Graphene is
considered to be a promising material for use in optoelectronic devices due to its fast response and broadband
capabilities. However, graphene absorbs only 2.3% of incident white light, which limits the performance of
photodetectors based on it. One promising approach to enhance the optical absorption of graphene is the use of
plasmonic resonance. The field of plasmonics has been receiving considerable attention from the viewpoint of both
fundamental physics and practical applications, and graphene plasmonics has become one of the most interesting topics
in optoelectronics. In the present study, we investigated the optical properties of graphene on a plasmonic metamaterial
absorber (PMA). The PMA was based on a metal-insulator-metal structure, in which surface plasmon resonance was
induced. The graphene was synthesized by chemical vapor deposition and transferred onto the PMA, and the reflectance
of the PMA in the infrared (IR) region, with and without graphene, was compared. The presence of the graphene layer
was found to lead to significantly enhanced absorption only at the main plasmon resonance wavelength. The localized
plasmonic resonance induced by the PMA enhanced the absorption of graphene, which was attributed to the
enhancement of the total absorption of the PMA with graphene. The results obtained in the present study are expected to
lead to improvements in the performance of graphene-based IR detectors.
Although standard uncooled infrared (IR) sensors can be used to record information such as the shape, position, and
average radiant intensity of objects, these devices cannot capture color (that is, wavelength) data. Achieving wavelength
selectivity would pave the way for the development of advanced uncooled IR sensors capable of providing color
information as well as multi-color image sensors that would have significant advantages in applications such as fire
detection, gas analysis, hazardous material recognition, and biological analysis. We have previously demonstrated an
uncooled IR sensor incorporating a two-dimensional plasmonic absorber (2D PLA) that exhibits wavelength selectivity
over a wide range in the mid- and long-IR regions. This PLA has a 2D Au-based periodic array of dimples, in which
surface plasmon modes are induced and wavelength-selective absorption occurs. However, the dependence of the
absorption bandwidth on certain structural parameters has yet to be clarified. The bandwidth of such devices is a vital
factor when considering the practical application of these sensors to tasks such as gas detection. In the present study,
control of the bandwidth was theoretically investigated using a rigorous coupled wave analysis approach. It is
demonstrated that the dimple sidewall structure has a significant impact on the bandwidth and can be used to control
both narrow- and broadband absorption. Increasing the sidewall slope was found to decrease the bandwidth due to
suppression of cavity-mode resonance in the depth direction of the dimples. These results will contribute to the
development of high-resolution, wavelength-selective uncooled IR sensors.
High-performance wavelength-selective infrared (IR) sensors require small pixel structures, a low-thermal mass, and operation in the middle-wavelength infrared (MWIR) and long-wavelength infrared (LWIR) regions for multicolor IR imaging. All-metal-based mushroom plasmonic metamaterial absorbers (MPMAs) were investigated theoretically and were designed to enhance the performance of wavelength-selective uncooled IR sensors. All components of the MPMAs are based on thin layers of metals such as Au without oxide insulators for increased absorption. The absorption properties of the MPMAs were investigated by rigorous coupled-wave analysis. Strong wavelength-selective absorption is realized over a wide range of MWIR and LWIR wavelengths by the plasmonic resonance of the micropatch and the narrow-gap resonance, without disturbance from the intrinsic absorption of oxide insulators. The absorption wavelength is defined mainly by the micropatch size and is longer than its period. The metal post width has less impact on the absorption properties and can maintain single-mode operation. Through-holes can be formed on the plate area to reduce the thermal mass. A small pixel size with reduced thermal mass and wideband single-mode operation can be realized using all-metal-based MPMAs.
Three-dimensional plasmonic metamaterial absorbers (3-D PMAs) based on all-metal structures were developed. 3-D PMAs consist of a periodic array of thin metal micropatches connected to a thin metal plate with narrow metal posts. The 3-D PMA consists of plasmonic metal (Au) based components. 3-D PMAs were fabricated by a two-step lift-off procedure with a carbon sacrifice layer and a narrow metal post with a height of 200 nm was achieved. Reflection spectroscopy measurements demonstrate that the wavelength-selective absorption was realized, and the absorption wavelength can be controlled by the micropatch size, regardless of the micropatch-array period, and can be longer than the micropatch array period. Wavelength selective absorption is possible due to the surface plasmonic resonant mode localized at the micropatches. The metal posts have negligible impact on the plasmonic resonance. 3-D PMAs based on all-metal structures can be applicable for a wide range of the middle- and long-wavelength IR region due to the lack of additional absorption by an insulator layer based on SiO2, SiN, or Al2O3, which are typically used in metal-insulatormetal absorbers. 3-D PMAs have a small thermal mass and an absorption wavelength beyond the period, which result in a fast response and small pixel size. The results obtained here should contribute to the high-performance wavelengthselective uncooled IR sensors and IR emitters.
A polarization-selective uncooled infrared (IR) sensor has been developed based on a one-dimensional plasmonic grating absorber (1-D PGA). The 1-D PGA has an Au-based one-dimensional periodic grating structure, where photons can be manipulated by surface plasmon resonance. A microelectromechanical systems-based uncooled IR sensor was fabricated using the 1-D PGA with complementary metal oxide semiconductor (CMOS) and micromachining techniques. The 1-D PGA was formed with an Au layer sputtered on a grating pattered SiO2 layer. An Al layer was then introduced onto the backside of the 1-D PGA to reflect scattered light and prevent absorption at the SiO2 backside of the absorber. The responsivity could be selectively enhanced depending on the polarization and the grating direction, and an absorption wavelength longer than the surface period and broadband absorption were realized due to the effect of the resonance in the grating depth direction. The 1-D PGAs enable a detection wavelength longer than the period and broadbandpolarization- selectivity by control of the grating depth in addition to the period. The results obtained in this study will contribute to the advancement of polarimetric IR imaging.
A polarization-selective uncooled infrared (IR) sensor was developed based on an asymmetric two-dimensional plasmonic absorber (2-D PLA). The 2-D PLA has an Au-based 2-D periodic dimple structure, where photons can be manipulated by spoof surface plasmon polaritons. Asymmetry was introduced into the 2-D PLA to realize a polarization selective function. Numerical investigations demonstrate that a 2-D PLA with ellipsoidal dimples (2-D PLA-E) gives rise to polarization-dependent absorption properties due to the asymmetric dimple shape. A microelectromechanical systems-based uncooled IR sensor was fabricated using a 2-D PLA-E through complementary metal oxide semiconductor (CMOS) and micromachining techniques. The 2-D PLA-E was formed with an Au layer sputtered on a SiO2 layer with ellipsoidal holes. The dependence of the responsivity on the polarization indicates that the responsivity is selectively enhanced according to the polarization and the asymmetry of the ellipsoids. The results provide direct evidence that a polarization-selective uncooled IR sensor can be realized simply by the introduction of asymmetry to the surface structure of the 2-D PLA, without the need for a polarizer or optical resonant structures. In addition, a pixel array where each pixel has a different detection polarization could be developed for polarimetric imaging using standard CMOS and micromachining techniques.
A three-dimensional plasmonic metamaterial absorber (3-D PMA) was theoretically investigated and designed for the performance enhancement of wavelength selective uncooled infrared (IR) sensors. All components of the 3-D PMA are based on thin layers of plasmonic metals such as Au. The post produces a narrow gap, such as a few hundred nanometers, between the micropatch and the metal plate. The absorption properties of the 3-D PMA were investigated by rigorous coupled-wave analysis. A strong wavelength selective absorption is realized by the plasmonic resonant mode of the micropatch and the narrow-gap resonant mode between the micropatch and the plate. The disturbance of the post for both resonance modes is negligible. The absorption wavelength is defined mainly by the size of the micropatch, regardless of the micropatch array period and is longer than the micropatch array period. The absorption mode can also be controlled by the shape of the micropatch. Through-holes can be formed on the plate area, where there is no gap resonance to the micropatch. The thickness of each component can be reduced considering the skin depth effect and there is no added absorption of materials such as SiO2. A small pixel size with reduced thermal mass can be realized using a 3-D PMA structure. The results obtained here will contribute to the development of high-performance uncooled IR sensors for multicolor imaging.
A polarization-selective uncooled infrared (IR) sensor has been developed based on an asymmetric two-dimensional plasmonic absorber (2-D PLA). The 2-D PLA has a Au-based 2-D periodic dimple structure, where photons can be manipulated by spoof surface plasmon polaritons. Asymmetry was introduced into the 2-D PLA to realize a polarization selective function. Numerical investigations demonstrate that a 2-D PLA with ellipsoidal dimples (2-D PLA-E) gives rise to polarization-dependent absorption properties due to the asymmetric dimple shape. A microelectromechanical systems-based uncooled IR sensor was fabricated using a 2-D PLA-E through a complementary metal oxide semiconductor (CMOS) and micromachining techniques. The 2-D PLA-E was formed by a Au layer sputtered on a SiO2 layer with ellipsoidal holes. An Al layer was then introduced on the backside of the 2-D PLA-E to reflect scattered light and prevent absorption at the SiO2 substrate. Measurement of the responsivity dependence on the polarization shows that the responsivity is selectively enhanced depending on the polarization and the asymmetry of the ellipse. The results provide direct evidence that a polarization-selective uncooled IR sensor can be realized simply by introducing asymmetry to the surface structure of a 2-D PLA without any polarizer or optical resonant structures. In addition, a pixel array where each pixel has a different detection polarization could be developed for polarimetric imaging using standard CMOS and micromachining techniques.
A wavelength selective wideband uncooled infrared (IR) sensor that detects middle-wavelength and long-wavelength IR (MWIR and LWIR) regions has been developed using a two-dimensional plasmonic absorber (2-D PLA). The 2-D PLA has a Au-based 2-D periodic dimple-array structure, where photons can be manipulated using a spoof surface plasmon. Numerical investigations demonstrate that the absorption wavelength can be designed according to the surface period of dimples over a wide wavelength range (MWIR and LWIR regions). A microelectromechanical system-based uncooled IR sensor with a 2-D PLA was fabricated using complementary metal oxide semiconductor and micromachining techniques. Measurement of the spectral responsivity shows that the selective enhancement of responsivity is achieved over both MWIR and LWIR regions, where the wavelength of the responsivity peak coincides with the dimple period of the 2-D PLA. The results provide direct evidence that a wideband wavelength selective IR sensor can be realized simply by design of the 2-D PLA surface structure without the need for vertical control in terms of gap or thickness. A pixel array where each pixel has a different detection wavelength could be developed for multicolor IR imaging.
A wavelength selective wideband uncooled infrared (IR) sensor that detects middle-wavelength and long-wavelength
infrared (MWIR and LWIR) regions has been developed using a two-dimensional plasmonic absorber (2D PLA). The
2D PLA has a Au-based 2D periodic hole-array structure, where photons can be manipulated using the surface plasmonlike
mode. Numerical investigations demonstrate that the wavelength of the absorption can be designed according to the
surface period of holes over a wide wavelength range (MWIR and LWIR regions). A microelectromechanical system
(MEMS)-based uncooled IR sensor with a 2D PLA was fabricated using complementary metal oxide semiconductor
(CMOS) and micromachining techniques. The 2D PLA was formed from a Au layer sputtered on a perforated oxide
layer. A reflection layer was introduced to the backside of the 2D PLA to prevent additional absorption. Measurement of
the spectral responsivity shows that selective enhancement of responsivity is achieved over both MWIR and LWIR
regions, where the wavelength of the responsivity peak coincides with the hole period of the 2D PLA. The results
obtained here provide direct evidence that a wideband wavelength selective IR sensor can be realized simply by design
of the 2D PLA surface structure without the need for vertical control in terms of gap or thickness. A pixel array where
each pixel has a different detection wavelength would be developed for multicolor infrared imaging using standard
CMOS and micromachining techniques.
Various important scientific and engineering applications, such as control of spontaneous emission, zero-threshold lasing, sharp bending of light, and trapping of photons, are expected by using photonic bandgap (PBG) crystals with artificially introduced defect states and/ or light-emitters. Realizing the maximum potential of photonic crystals requires the following steps: (i) construct a three-dimensional (3D) crystal with a complete photonic bandgap in the optical wavelength region; (ii) introduce an arbitrary defect into the crystal at an arbitrary position; (iii) introduce an efficient light-emitter; and, (iv) use an electronically conductive crystal, as this is desirable for actual device application. Although various approaches to constructing 3D crystals have been proposed and investigated, none of these reports satisfies the above requirements simultaneously. To develop complete 3D crystals at infrared (5-10um) to near-infrared wavelengths (1-2um), we stacked III-V semiconductor gratings into a diamond structure by means of wafer bonding and a laser-beam-assisted very precise alignment technique. Since the crystal is constructed with III-V semiconductors, which are widely used for optoelectronic devices, requirement (iii) is satisfied. Moreover, as the wafer bonding enables us to construct an arbitrary structure and to form an electronically conductive interface, all the above requirements (i)-(iv) will be satisfied. In this paper, we review our approach for creating full 3D photonic bandgap crystals at near-infrared wavelengths.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.