Ga2O3 has established to be a promising material for deep UV and UV optoelectronics and sensing applications. However, a major drawback of Ga2O3 thin film based optoelectronic devices is the existence of native point defects which can result in the creation of sub-bandgap absorption, carrier scattering centres, and leakage channels and becomes an obstruction to their efficient device applications. To overcome this high temperature annealing processes are required which not only leads to a rise in the thermal budget but also put many fabrication and technological bounds in device fabrication. Therefore, in this work we report room temperature ultraviolet-ozone (UVO) annealing as a facile and cost-effective method which can control defect states and improve the optical efficiency of Ga2O3 thin film. The Ga2O3 thin films were deposited by radio frequency (RF) sputtering technique on p-Si at room temperature. The grown films were subsequently subjected to UV-Ozone (UVO) annealing for 30, 50, 70, and 90 min at room temperature. The atomic force microscopy result shows the impacts of UV-Ozone (UVO) annealing time on the film roughness which further associated with reduced oxygen vacancies (Vo) concentration. Optimum time of UVO annealing for Ga2O3 thin films was estimated to be 50 min. Finally, the variation in current-voltage (I-V) characteristics of Ga2O3/p-Si heterojunctions are estimated to understand the effect UVO annealing on its electrical properties of RF sputtered Ga2O3 thin film.
ZnO is a fascinating large gap (3.37 eV) semiconductor, which exhibits intrinsically n-type conductive due to its native defects such as zinc interstitials and oxygen vacancies and such n-type related defects tend to compensate the p-type acceptor defects. However, the generation process of p-type defects is more challenging for developing a good quality homojunction optical device. Here we have studied the effect of ex-situ atmospheric annealing on conductivity of ZnO films. The ZnO films were deposited using RF sputtering on Si substrate temperature at 400°C substrate temperature and 2.2E-2 mbar gas pressure. The films were deposited in oxygen-rich ambient to achieve less oxygen vacancy defects in the film. The ex-situ atmospheric annealing is performed at higher temperature of 900 and 1000ºC. The effects of this postdeposition annealing on the electrical, structural, elemental and optical properties of ZnO thin films were investigated in detail. The X-ray Diffraction (XRD) results exhibited the hexagonal wurtzite structure (002) orientation. After annealing, the XRD peak is shifted at higher 2-thetha value, which indicates a reduction in lattice constant. Further, X-ray photoelectron spectroscopy (XPS) had been done and such XPS results confirmed that simultaneous generation of acceptor defects and reduction of oxygen vacancy related donor concentrations. The electrical properties of films were studied using hall measurement system. These electrical parameters were purposive to inspect the effect of ex-situ atmospheric annealing temperatures on conductivity of films. The Hall measurement confirmed that 1000ºC annealed films achieve p-type conductivity with high reproducibility and such p-type behavior exhibits high mobility. Thus, temperature induced conductivity reversal could be a potential and cost-effective technique to achieve highly stable p-type ZnO films.
ZnO is a fascinating wide gap (3.37 eV) semiconductor due to its tunable optical and electrical properties, which can be utilized for several nanodevices such as nanogenerators, photodetectors, sensors, lasers, and TFTs. In this study, we have investigated the effect of the incorporation of dopants on the native defects and corresponding optical properties of ZnO. We have prepared three samples for the current study and such samples are named samples Z-0, Z-1, and Z-2 for undoped ZnO film, undoped ZnO film annealed at 800°C, and phosphorus doped ZnO film by using spin-on dopant method at an elevated temperature of 800°C, respectively. The XRD results show a dominant peak along the (002) plane for all samples. The room-temperature photoluminescence spectra reveal that the broad peak around 542 nm for sample Z-0 gradually shifts towards the UV region for samples Z-1 and Z-2 and appears around 509 nm and 413 nm, respectively. Significantly, such blue emission is associated with the transitions from oxygen vacancies to valence band or zinc interstitial to valance band. Also, relatively huge reductions in oxygen vacancies are observed in phosphorus doped ZnO films as compared with undoped and undoped-anneal films. Further, we have verified such reductions in oxygen vacancies with XPS O-1s spectra-related peaks (~531-532 eV) with high-temperature annealing and phosphorus doping. Therefore, such a type of oxygen vacancy reduction in ZnO films by cost-effective SOD doping technique is highly essential for developing several ZnO-based functional devices.
The deep UV photodetectors (DUV-PDs) are technologically important for diverse applications, ranging from environmental monitoring, space communication etc. Among all solar blind materials Ga2O3 thin film shows its strong contention owing to its intrinsic solar-blind nature. However, the PD’s efficiency can be significantly affected by the defects such as oxygen vacancies (VO). Both the deficiency and surplus of oxygen during Ga2O3 thin film deposition can result in the formation of carrier scattering centers, sub-bandgap absorption, and leakage channels. In this work, we have studied the impact of oxygen flow rate (OFR) on the optical and electrical properties of RF sputtered Ga2O3 thin film. The Ga2O3 thin films were deposited on p-Si at room temperature, where the Ar to O2 ratio has been varied from 1:0, 1:1, to 1:2 to maintain the O2 poor and O2 rich condition. The XRD spectrum shows the presence of two peaks positioned at ~33.0° , and ~64.5° , which are further identified as β(-202), and β(-313), respectively for samples grown without oxygen. The top view FESEM images confirm the uniform film growth for both O2 rich conditions while some isolated bubble-like and grain-like structures are witnessed in ratios 1:0, and 1:1, respectively. The change in optical bandgap for all the samples is determined using diffuse reflectance spectra which show the bandgap values lie in the range of 4.1 eV-4.2 eV. Furthermore, the deconvoluted photoluminescence spectra (in the range of λ=300-500 nm) show the change in different types of Vo defects originating due to OFR induced structural asymmetry in the Ga2O3 thin film. Finally, the change in dark current in Ga2O3/p-Si heterojunctions is estimated from current-voltage (I-V) characteristics to understand the effect of OFR on its electrical properties for future DUV detectors.
In the current study, we report the growth of rare earth Er-doped Ga2O3 nanostructures on Ga2O3- seeded Si substrate by employing chemical bath deposition (CBD) and RF magnetron sputtering techniques. A thin layer (~50 nm) of Ga2O3 is deposited on p-Si substrate with the optimize deposition temperature and Ar:O2 flow rate to create a favourable template for growing high quality nanostructures on it. After growing the Er-doped Ga2O3 nanostructures, thermal annealing is performed at 800°C to achieve thermodynamically stable β-phase of Ga2O3. The effect of Er doping on structural, optical and luminescence properties of Ga2O3 nanostructures has been successfully investigated by employing FEGSEM, XRD, UV-VIS and PL. XRD studies confirms the polycrystalline β-phase monoclinic structure of Ga2O3 for both undoped and Er-doped nanostructures with dominant <-111> plane. Top view images of FEGSEM depict the large area growth of rod/wire like structures of Ga2O3 on thin Ga2O3 deposited Si substrate and confirm the formation of heterojunction between Ga2O3 and Si. Deconvoluted PL spectra shows two broad peaks within the wavelength range of 260 nm to 460 nm, which are associated with near band emission and three different types of oxygen vacancies present in β-Ga2O3, respectively. The change in optical absorbance and corresponding energy band gap of undoped and Er-doped nanostructures are analysed in detail by using UV-VIS spectroscopy and such energy bandgap values lie with the range of 4.4 eV-4.7 eV. Finally, current-voltage characteristics of undoped and Er-doped Ga2O3/Si heterojunction has been studied and such heterojunctions can be a potential candidate for the fabrication of several optoelectronic devices as well as high power applications.
Gallium oxide (Ga2O3) is an emerging wideband semiconductor which can be utilize in solar-blind photodetector and high power electronics application. Having a large bandgap and high breakdown field makes Ga2O3 material suitable for these device applications. However, the physical and the optical properties of Ga2O3 can be tailored by changing the annealing ambient and temperature, and understanding how the annealing atmosphere can affect these properties is crucial for designing a next generation optoelectronic devices. Moreover, the presence of defects and impurities can also affect the device parameters. Thus, in this work, we have investigated the influence of post deposition annealing atmosphere on the morphological, structural, and optical properties of Ga2O3 films. The prepared samples were further went through thermal annealing at 800°C for 30 mins in nitrogen (N2), and oxygen (O2) ambient to achieve β-phase of Ga2O3. The structural properties of all the samples were studied by atomic force microscopy, and x-ray diffraction while the optical properties were studies by UV-visible, and photoluminescence spectroscopy. We have found monoclinic β-phase in the polycrystalline annealed Ga2O3 samples. The optical band gap of films were increased after annealing and highest band gap is obtained to 5.44eV in N2 annealed sample as compared to as-deposited sample (4.56eV). A broad photoluminescence spectrum ranged from 350 to 480 nm was observed, which further deconvoluted in three peaks at around 378 nm, 399 nm, and 422 nm in as-deposited sample. The same peaks with broad photoluminescence spectrum was found to be blue shifted for annealed samples as compared to the as-deposited. This study will open a new direction in future deep-UV photodetector fabrication.
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.