Research On Type-Ⅱ Superlattice Infrared Detector Performance

Type-Ⅱ InAs/GaSb superlattice has been the most potential material system as thethird generation IR photon detector, because of its adjustable energy gap, highereffective mass of electrons and holes, lower Auger recombination rates, advanced Ⅲ-Ⅴgrowth and processing technology. The focus of this paper is mainly about the modelingand design of Type-Ⅱ InAs/GaSb superlattice energy gap structure, the growing andstructural performance test of superlattices and the fabrication of Type-Ⅱ InAs/GaSbsuperlattice detector.The modeling shows that the period of InAs and GaSb layer（m or n） has differentinfluence on InAs/GaSb（mML/nML） superlattice’s energy gap. When the period ofGaSb layer was set on8ML and the period of InAs layer was changed from4ML to16ML, the energy gap changed a lot while the cut-off wavelength changed from2.5μmto14μm, which covers three atmospheric window: short wave, medium wave and longwave. Conversely, when the period of InAs layer was set on8ML and the period ofGaSb layer was changed from4ML to16ML, the energy gap changed a little and thecut-off wavelength changed less than1μm. Therefore，in the design of superlatticestructure, a big change of the period of InAs layer means adjustable energy gap while aappropriate change of the period of GaSb layer decide a low strain and a high crystalquality.After the design, several InAs/GaSb superlattices were grown, including differentspectrum response of short, medium and long wave. The structural performance testshows that the period thickness of six sample have little difference with the modelingresult, non-uniformity is less than1%and the strain ε=Δd/d is lower than10^-3, all ofwhich indicate that the lattice matching of InAs and GaSb layer is mainly achieved. TheFWHM of the superlattice zero diffraction peak is on arc second level, which indicates alow dislocation density and a high crystal quality. So as the AFM test shows, the RMSroughness is less than0.6nm. The PL spectrum shows the peak luminous wavelength ofshort, medium and long wave sample is2.855μm、4.368μm、10.077μm, relativelycoinciding with modeling result.A wet chemical etching solution based on H₃PO₄/C₆H₈O₇/H₂O₂/H₂O was studiedby using lithography. Finally the solution was confirmed as H₃PO₄:2mL/C₆H₈O₇:1g/ H²O2:5mL/H²O:400mL， which has a appropriate etching speed of100nm/min withInAs, GaSb and superlattice and shows smooth interface. The specificcontactresistances under different annealing condition was studied using TLM. Theohmic contact resistance between Ti/Au with InAs and GaSb achieve10^-4and10^-5Ω·cm².The test of single-unit semiconductor device’s infrared detection performanceindicate that, the cutoff wavelength of medium and long wave infrared detector are4.5μm and14μm respectively. And at77K, the blackbody detectivity of medium andlong wave type-Ⅱ InAs/GaSb superlattice reached values of2.37*10¹0cm Hz^1/2·W^-1and4.26*10⁹cm Hz^1/2·W^-1respectively.This paper focus on the modeling of energy gap, the design and grow of materialand the fabrication and performance test of the detector. Type-Ⅱ InAs/GaSb superlatticesingle-unit detector was finally achieved. Advantages and application value of type-ⅡInAs/GaSb superlattice has finally been found in infrared detection field by structureperformance and detection performance test.