Herein, we report a novel approach to passivation of InAs/GaSb superlattice for mid-short wavelength dual-color infrared detector. One of the major challenges faced by InAs/GaSb superlattice devices arises owing to the large number of surface states that are generated. Surface passivation and subsequent capping of the surfaces are absolutely essential for any practical applicability of this material system. As evidenced by the comparison of unpassivated and passivated InAs/ GaSb superlattice mid-short wavelength dual-color infrared photodiodes. The surface passivation methods include zinc sulfide (ZnS) coating after anodic oxide, and ZnS coating after fluoride passivation. InAs/GaSb superlattice infrared materials were grown by molecular beam epitaxy on GaSb (100) substrates. A GaSb buffer layer, which can decrease the occurrence of defects with similar pyramidal structure, was grown for optimized superlattice growth condition. The reliability of passivation by anodic fluoride was confirmed by AES. The leakage current as a function of bias voltage (J–V) for superlattice diodes obtained using different passivation methods has been examined at 77 K. The best performance was demonstrated by the ZnS after anodic fluoride passivation.
The InSb epitaxial layer of p+-n-n+ structure was grown by Molecular Beam Epitaxy (MBE) on a heavily doped InSb substrate. Photodiodes of InSb were fabricated by standard semiconductor manufacturing process. Measurement and analysis of its electrical properties was carried out. Compared with traditional bulk crystal InSb of p+-n structure, we find that, when the external bias voltage is 0.1V, dark current density values of p+-n-n+ InSb device and InSb bulk material device is 1.1×10-6 A·cm-2 and 9.5×10-5 A·cm-2 at 77K, respectively. zero-bias-resistance area products is 8.9×104Ω·cm2 and 6.2×103 Ω·cm2 at 77K, respectively. Doping concentrations values in the absorption layers are equal to 5.0×1014 cm-3 and 1.3×1016 cm-3 , respectively. The InSb epitaxial layer of p+-n-n+ structure which has better crystal quality achieves better performance than bulk crystal InSb when the passivation process is reliable. It provides an important foundation for the fabrication of epitaxial InSb infrared detector.
Infrared(IR)photo detectors based on InAs/GaSb type II superlattice have developed quickly in recent years. Many groups show great interest in InAs/GaSb superlattice detector for its superiors as high quantum efficient, high working temperature, high uniformity and low dark current densities. Inductively coupled plasma(ICP) etching of GaSb and InAs/ GaSb superlattices were performed using Cl2/Ar/CH4/H2. This paper introduceste inductively coupled plasma( ICP) etching of Inas/GaSb with SiO2 mask by the Cl2/Ar/CH4/H2 mixed-gas process. The effects of process parameters such as gas combination, ICP and RF power on the etch rate and quality of InAs/GaSb It is found that the ratio of Cl2 flow rate significantly affects the etch rate, due to the trade-off between physical and chemical component of etching. The etch rate of InAs/GaSb increases with the increase of percent of Cl2, there will InClx remains in the etching channel when the etching depth exceeded 2μm, which can stop the etching going on. This phenomenon can be eliminated by decrease the Cl2 ratio,to make sure the etching depth reach 6μm under a certain low etching rate. The surface morphology and SEM of the superlattice material after etching shows that dry etching morphology is better than wet etching.After the electrode is grown, the superlattice chip have a good diode characteristic curve.
One of the major challenges of InAs/GaSb superlattice devices arises owing to the large number of surface states generated during fabrication processes. Surface passivation and subsequent capping of the surfaces are essential for any practical applicability of this material system. In this paper, we passivated InAs/GaSb superlattice infrared detectors proposed anodic fluoride passivation method. Short and mid wavelength InAs/GaSb superlattice infrared materials were grown by Molecular Beam Epitaxy (MBE) on GaSb (100) substrates. A GaSb buffer layer was grown for optimized superlattice growth condition, which can decrease the occurrence of defects with similar pyramidal structure. The result of auger electron spectroscopy (AES) surface scans after anodic fluoride passivation confirms that anodic fluoride passivation treatment did affect. The leakage current as a function of bias voltage (I-V) for InAs/GaSb superlattice infrared detectors has been examined at 77K. Compared with the unpassivated approach, this passivation methods decrease the dark current by approximately five orders of magnitude.
Type II InAs/GaSb superlattice material, because of its excellent predominance, is becoming the best choice for the third generation infrared detector. Surface passivation, which is one of the most important process during the device fabricated, can improve the performance of superlattice detector greatly. In this work, three passivation methods were experimented based on MWIR superlattices, then after electrodes were fabricated, detectors were tested. From the measurements, the passivation of anodic sulfide cooperating with SiO2 is more effective than others, zero-bias resistance area product of device with 5μm cutoff wavelength reach up to 104Ω•cm2 at 77K, reverse-bias dark current density is reduced to 10-5A/cm2 at -1V, peak detectivity is 1010cm•Hz1/2/W and quantum efficiency reach 35%. Retest after a month later, the performance of photodiodes without diversity.
A series of InSb thin films were fabricated on the sapphire substrate by femtosecond pulsed laser deposition (fsPLD)
method with the laser of 110 fs pulse width. The laser incident energy is near 1mJ. The target is one kind of heavily
doped n-type InSb. The substrate temperature changes from 80 ºC to 400 ºC, Laser frequency changes from 1 Hz to 1 kHz and laser energy density changes from 0.1 J/cm2 to 1 J/cm2. The effects of different laser frequencies, substrate temperature and laser energy density on the surface morphology and optical property have been investigated separately. The surface morphology of InSb thin films was observed by metallurgical microscope and scanning electron microscope (SEM). The thin film with better surface morphology is obtained when the laser frequency is 10 Hz, substrate temperature is 80 ºC and laser energy density is 0.1 J/cm2. X-ray diffraction (XRD) demonstrates that the InSb thin film has a good single crystal structure. The infrared transmittance of InSb thin films is measured by an infrared spectrometer. The results show that good InSb thin films can be prepared by fsPLD. It is found that the mid-wavelength Infrared transmission through the InSb thin films is near 55% and it almost does not change under the different growing conditions.
Inductively coupled plasma (ICP) etching of GaSb and InAs/GaSb super lattices were performed using Cl2/Ar plasma. The effects of GaSb of etching time, Cl2: Ar ratio and RF power on etching rates were investigated. It is found that the etching rates were relatively low when etch time was less than 2 min, After etching for 3 min, the etching rates was about 1.3 μm/min as a result of constant, also, the etching rate was increased monotonically with the increasing of Cl2 proportion, and reaches at 4.14 μm/min when the Cl2 concentration is 80%. In contrast, the peak value of etching rate of InAs/GaSb super lattices is 1.37 μm/min and the increase extent of etching rates of InAs/GaSb super lattices was much lower than that of GaSb, mainly owing to the insensitivity of InAs to the Cl2 concentration. In addition, the etching rates of GaSb increased slowly with the increasing of RF power, which indicated the less efficiency influence of RF power on etching rate. The surface morphology of etched InAs/GaSb super lattices was characterized by WYKO HD3300 head measurement system, which suggested that the surface morphology was becoming rough with the increase of Cl2 percentage. When the concentration reaches 60%, the surface morphology was unacceptable. The results showed that contrast to wet chemical etching, dry etching can form smoother pattern, which indicates the promising application in fabricating fine devices.
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