Study On Defects And Photoelectric Properties Of Antimonide Superlattice Materials

InAs/GaSb type-? superlattice has many theoretical advantages in the preparation of infrared detectors,and is one of the third-generation infrared focal plane preferred material systems recognized internationally.At present,the mainstream InAs/GaSb T2SL detection materials are usually grown on GaSb substrates,and after more than ten years of development,InAs/GaSb superlattice detection technology has made great progress,and the performance of super-lattice detectors reported are comparable to mercury cadmium telluride detectors so far.Many research institutions in the world have realized many types of superlattice focal plane devices,covering short-wave,medium-,long-wave,very long-wave,two-color,multi-color,high-temperature,large-scale,etc,related devices began engineering applications and products manufacturing,superlattice detection technology has become an important development direction of the new generation of infrared detection technology.However,although the theoretical performance of the superlattice is an order of magnitude higher than that of mercury cadmium telluride,the surface atom diffusion coefficient is small due to its low growth temperature and large lattice mismatch of InAs/GaSb type-? superlattice.Scientific and technical problems such as short,high defect density,high defect-assisted tunneling current and short lifetime of the minority,make the performance and theoretical expectations still have a certain gap.Therefore,in order to continuously improve the performance of superlattice detectors and obtain theoretically expected performance of superlattice detectors,in recent years,the superlattice research team of the Shanghai Institute of Technical Physics of the Chinese Academy of Sciences began to explore the growth study of InAs/Ga?As?Sb type-? superlattice materials.The InAs/Ga?As?Sb type-? superlattice epitaxially grown on the InAs substrate can achieve higher growth temperatures,and theoretically it is easier to obtain a low-defect superlattice epitaxial layer.More importantly,for InAs/Ga?As?Sb T2SL,the mismatch between the epitaxial superlattice layer and the substrate can be adjusted by adjusting the content of As in Ga?As?Sb.There is no need to insert a specific interface layer.Moreover,as the infrared detector develops into long-wave and very long-wave,the thickness of the InAs layer in the superlattice increases correspondingly,and the growth of the superlattice on the InAs substrate does not need to considere the strain between substrate and epitaxial layer due to the increase in the thickness of the InAs,therefore,the use of MBE technology for the growth of InAs/Ga?As?Sb type-? superlattice can theoretically achieve a higher quality epitaxial material,which is important for the further development and technical application of superlattice infrared detection technology.In view of this,this paper focuses on a series of in-depth research on the defects and photoelectric properties of InAs/Ga?As?Sb T2SL materials.Moreover,the paper also conducted an exploratory research on the new superlattice avalanche photodetectors.The specific research contents and progress are as follows:1.Study on defect characteristics of InAs and GaSb bulk materials.Through the optimization of wet chemical etchant composition and ratio,the etch pit morphology of?100?crystal plane of InAs and GaSb bulk materials are clearly revealed,and etch pit density is in the order of 10⁴.Through transmission spectrum test,and fitting analysis of absorption coefficient with wavelength,the results show that the absorption of infrared radiation by free electrons in n-type InAs substrate is dominated by the scattering mechanism of ionized impurities.Transmittance tests were performed on InAs substrates of different thicknesses,indicating the transmittance increased as the thickness is reduced.When the thickness is reduced to about 200?m,a Fabry-Perot cavity is formed between the substrate and the air layer,resulting in a oscillating effect of transmittance with wavelength.Through the test of variable temperature transmission spectrum,it is show that the increase of temperature has little effect on the infrared absorption of InAs.2.Photoluminescence properties of InAs/Ga?As?Sb type-? superlattice materials.Through the testing and analysis of the variable-temperature PL spectrum,it is found that the full-width at half maximum?FWHM?of the new InAs/Ga?As?Sb superlattice material with similar luminescence peak wavelength is narrower than that of InAs/GaSb material over the entire temperature range.The rate of FWHM becomes wider as the temperature rises,the FWHM of all materials is dominated by the non-uniform portion,which is mainly related to the variation of well width of type-? superlattice,internal impurities and interface roughness.The fitting analysis of PL integral intensity of the luminescence peaks of InAs/Ga?As?Sb and InAs/GaSb T2SL are all consistent with the two-channel non-radiative composite model and the fitting results show that the defect contribution of the new InAs/Ga?As?Sb T2SL material in the smilar wavelength is reduced because of the contribution of the non-radiative recombination channel relate to defect energy that lead to PL intensity quenching is reduced.3.Study on wet etching process of InAs/Ga?As?Sb type-? superlattice cell devices.The wet etching of InAs,GaSb binary compunds and new InAs/Ga?As?Sb T2SL materials was systematically studied,and the etchant was optimized.The smooth etched surface and steep sidewalls of InAs/Ga?As?Sb T2SL material were obtained by optimized etchant.The surface roughness was only 1 nm and a long-wave InAs/Ga?As?Sb.T2SL cell device was prepared.The devices were tested for spectral response,I-V,and blackbody response.At 81 K,the 50%cutoff wavelength was 12?m,the peak current response rate was 1.6 A/W,and the corresponding peak quantum efficiency?QE?was 38%,the dark current density was 5.7×10^-3 A/cm² and the surface resistivity is 4.4×10³?cm,which is eight times higher than the unoptimized one.The experimental results show that the phosphate-based etchant can obtain long-wave InAs/Ga?As?Sb type-? superlattice infrared detector with low surface leakage.4.Exploratory study of InAs/GaSb superlattice infrared avalanche photodetectors.The advantages and applications of avalanche photodetector?APD?and the difficulties in preparing mid-infrared APD are introduced.The research status of InAs/GaSb superlattice APD and the advantages of preparing mid-infrared APD are described.Finally,the superlattice APD was prepared by the phosphoric acid wet etching process.The gain reached 120 when the bias voltage was about-11 V.Through the fitting of the noise spectrum,white noise was extracted,and the excess noise factor F was calculated,it is 2.2 at-5 V.