Study Of InAs/GaSb Films And Devices Properties

InAs/GaSb type-II superlattice materials are investigated for infrared photodetectorscapable of performance comparable. There is currently considerable interest inInAs/GaSb type-II superlattice because of their broken-gap type-II band alignment.InAs/GaSb type-II superlattices materials are widely used in civil applications andmilitary equipments as critical components of the system. Although it can be grownuntil recent years, there are few reports in the InAs/GaSb type-II superlattices infrareddetectors application. The surface passivation and mesa etching in the photodiodes stillneed much improvement.The materials were grown by solid source molecular beam epitaxy on high quality,large area substrate material GaSb. The main results are listed as the following:The influences of growth parameters like substrate temperatures (445℃-485℃),V/III ratios, sequences of shutters on the superlattice crystallization and optoelectronicproperties are investigated. InAs/GaSb superlattice with different periods8ML/8ML and4ML/8ML are obtained successfully. The easy tuning of the detecting wavelengths bychanging the periods of the superlattices is realized. The material quality of thesuperlattices has been improved significantly. To obtain well lattice matched and highinterface quality material, two shutter control methods (epitaxy-stop-method andmigration enhanced epitaxy) are applied in the growth of superlattice. InAs/GaSbsuperlattices with InSb-and mixed-like interfaces were grown at optimized growthtemperature. The results showed that superlattice grown at465℃had better crystalquality and smoother surface. Two kinds of interfaces were formed by controllingshutter sequences. X-ray diffraction and scanning electronic microscopy demonstratedthat superlattice with mixed-like interfaces were more sensitive to growth temperaturethan that with InSb-like interfaces. High quality superlattices were achieved, the surfaceroughness has reached1.7nm over an area of10μm×10μm, and the mismatch ofeip-layer is below0.13%.Shortwave and midwave InAs/GaSb superlattice IR photodetectors and photodiodeswere fabricated. The mesa etching techniques were studied using inductively coupledplasma (ICP) etching and wet chemical etching. ICP etching methods including CH4,Cl2and Ar based condition and wet etching methods including solution based on orthophosphoric acid and tartaric acid were compared. The results shows that CH4basedcondition can give a smooth surface and slippery lateral with an80degree angle.Furthermore, the mesa depth was easy to control. This method is suitable to fabricatedeep mesa device. It is also find that, solution based on orthophosphoric acid etchingcan obtain a smoother, clear surface and low longitudinal. It is a better way to fabricateinfrared FPA.Several surface passivation methods were used for type II InAs/GaSb superlatticedetectors herein. The methods include silicon dioxide (SiO2) coating after anodic sulfide,SiO2coating after anodic oxide, zinc sulfide (ZnS) coating after anodic sulfide and ZnScoating after ammonium sulfide chemical passivation. We also used a new passivationmethod (ZnS coating after anodic fluoride), this method was reported first time. Augerelectron spectroscopy tests were taken for confirm anodic fluoride treatment did affect.The leakage current as a function of bias voltage (I-V) for superlattice detectors obtainedhas been examined at77K. The reliability of etching technique and passivationprocessing are proved by I-V characterization of detectors. Compared with theunpassivated approach, passivation decrease the leakage current by approximately threeto five orders of magnitude. The R0A is3×105Ω cm2for midwave detectors and2×106Ω cm2for shortwave. The blackbody peak detectivity is3×1010cm·Hz1/2/W formidwave detectors and1.3×1011cm·Hz1/2/W for shortwave at77K.