Study On Lwir/Vlwir Detectors Of InAs/Ga(In)Sb Superlattice

In recent three decades, infrared detectors had a rapid development in military and civilian. Especially, the TapeⅡInAs/GaSb binary superlattice has an excellent material performance such as adjustable energy band structure(0~0.8ev), a wide range of wavelength response, high quantum efficiency, low Auger recombination rate and low dark current that made it the perfect materials for the Third-Generation Infrared Focal Plane Arrays detector.In this work, an adjustable wavelength response infrared detector of InAs/GaInSb SLs has been studied and the growth of SLs has been optimized and the characteristics of materials were examined and analyzed. The photoconductor devices fabrication was completed and the performances of the devices have also been studied. The main results are summarized as follows:(1)We use Riber Compact21 MBE equipment to growth InAs/GaInSb SLs grown on semi-insulating GaAs substrates. Through the optimized parameters we obtain the best temperature for growth: GaAs layer 600℃, the buffer layer (GaSb) 520℃, the SLs layer (InAs/GaInSb) 390℃. TheⅤ/Ⅲbeam ratio: Sb/Ga is 3 and the As/In is 10. According to the optimized condition, we designed three different types of samples that are: InAs/GaInSb (17ML/17ML)×30; InAs/GaInSb (17ML/7ML)×30 and InAs/GaInSb (7ML/17ML)×30; InAs/GaInSb (7ML/7ML)×30. The buffer layers are GaSb for 0.8μm thickness. The designed of response wavelength were 20μm, 12μm and 8μm according to the calculation by Empirical Tight-Binding Method experience potential function. The response wavelengths not only cover the very important atmospheric window in military applications, but also extended to the very long wavelength region that can be used for deep space exploration.We obtained the best in situ postgrowth annealing temperatures of 475℃by using atomic force microscopy (AFM) to observe the epitaxial film surface morphology. The results of DXRD and TEM observation showed that the SLs have an excellent structural quality such as a flat interface, a uniform period thickness and high crystalline quality. The samples'period thicknesses were 10.2nm, 7.2nm and 4.2nm. The value of x in Ga1-xInxSb alloy layer is 0.2. The non-uniformities of thickness and composition were less than 1.5%.(2)In this work, we mainly studied the lithography process of devices and the electrode preparation technology based on the high quality of the SL films and produced superlattice countertops photoconductor unit detectors successfully.Wet etching was used in lithography process of the device and tartaric acid corrosion system was suitable for this material system. The best ingredients are: tartaric acid (4g):H2O2 (3.5ml): HF (1.5ml):H2O (400ml). This corrosion system has a stable etching rate, good etching morphology and longitudinal etching. Au-Ni alloy was used for preparing the metal electrodes. The best annealing temperature is 380℃for ensuring ohmic contact. At this point, the I-V characteristic curve is linear relationship, indicating that the device has been formed for ohmic contact. If the annealing temperature is too low, the barrier between the electrode and materials will lead to bad ohmic contact and if the temperature is too high, it will damage the electrode that the device can not achieve ohmic contact. We theoretically discussed the mechanism of the dark current.(3)In this work, we also have studied the performance of the photoconductor detectors. The spectral response and blackbody tests were carried out at low temperatures. We also analyzed the SLs period thickness'affect on response wavelength.We use the Fourier Transform Infrared Spectroscopy and low temperature refrigeration system to test the spectral response of the devices at 10K to 77K. The results showed that the samples'spectral responses of the peak wavelength were 16μm, 10.8μm, 10μm and 7.1μm. The valve of the peak wavelength was shifted to the longer wavelength with increased the thickness of SL's thickness and the responsibility of the detector was decreased with increased the temperature. The number 3 device's peak directivity D* reaches 1.93×1010cm·Hz1/2·W-1 at 77K.