| The short wavelength infrared (SWIR) InGaAs detectors have been widely usedin space remote sensing, astronomical observation and spectral imaging, due to goodperformance such as high detectivity, good reliability, and so on,at relatively hightemperatures. In this paper, in order to further develop the application of SWIRInGaAs detectors in military and commercial field, in particularly the area of nightvision, the technology and device physics for the visible-short wavelength InGaAsdetectors have been researched. The chemical mechanical polishing (CMP) and wetchemical etching process for the InP substrate were investigated, and low-damageprocess parameters of substrate thinning were obtained. The32×32array detectorswere fabricated with different epitaxial materials, and then the influence of substratethinning process on the performance of array detectors, especially the responsespectrum, was studied.The effect of depositon of the anti-reflection (AR) coatingafter substrate thinning on the quantum efficiency (QE) and the dark current ofdetectors was researched. Physical model was used to analyze the influence ofmaterial parameters on the quantum efficiency of detectors. Finally, the512×128visible-short wavelength InGaAs focal plane array detectors were fabricated.The CMP process of InP substrate was studied, and the process parameters wereoptimized. The selectively wet etching of InP/InGaAs material was investigated.Based on the comparison of etching rates, SEM and AFM images of chemical wetetching of InP substrate with different ratios of etching solution and at differenttemparatures, the mixture solution of36.5%HCI:H3PO4with volume ratio of5:1at25℃was chosen as the etching solution for InP from InGaAs.And the solution oftartaric acid solution (composed of tartaric and H2O with wight ratio of1:1):H2O2with volume ratio of5:1at35℃was chosen for the etching solution of InGaAs fromInP.The32×32array detectors were fabricated with different epitaxial materialsinvolving an InAlAs buffer layer or an InP buffer layer.And then the process ofsubstrate thinning was applied to them.The results indicated that the removal of InPsubstrate with low damage could be aquired with combination of CMP and chemicalwet etching. The spectrum response of detectors was extended to visible light band,and the dark current almost remained the same.After substrate thinning process, thequantum efficiency of the detectors with InP buffer layer of0.2μm is approximately16%at500nm,54%at850nm,94%at1310nm and91%at1550nm.After the substrate removal process, a SiNx film was grown on the surface as theAR coating, by the ICP-CVD technology. The photoelectric characteristics ofdetectors indicated that the single SiNx thin film worked only in certain wavelengthbands and the response was enhanced. The dark current of the device wasunchanged.And then a SiNx/SiOx double-layer coating was designed aftersimulation from the software of SCI Company, and was deposited by the technologyof ICP-CVD, instead of the single-layer film.The results showed that the response of detectors was improved in the visible bands, as well as the short-wavelengthinfrared.The AR effect of SiNx/SiOx double-layer coating was better than the SiNxsingle-layer coating.The quantum efficiency of backside-illuminated planar InGaAs detectors wastheoretically simulated. The relationship between the thickness of the absorptionlayer and the quantum efficiency was analyzed.The simulated results for thedetectors with absorption layer of1.5μm and2.5μm corresponded with theexperiment results.With the increase of the thickness of absorption layer, the peakquantum efficiency increased rapidly at first, and then almost remained the same.Therelationships between material parameters including the thickness of the buffer layer,the thickness of the absorption layer, the doping concentration of the absorptionlayer and the quantum efficiency of the detectors after substrate thinning wereanalyzed.The resulsts indicated that the thickness of the InP buffer layer has the mostsignificant influence on the quantum efficiency in the visible spectrum.With theincrease of the thickness of the InP buffer layer,the useless absorption of InPincreased quickly, resulting in the sharp decrease of the quantum efficiency.Reducingthe thickness of the InP buffer layer was an effective way to improve the quantumefficiency of InGaAs detectors in the visible bands.The substrate removal process of large-area InGaAs focal plane array detectorswas studied. The512×128planar InGaAs focal plane array detectors were fabricatedon the epitaxial matrial with0.2μm InP buffer layer.The photoelectric characteristicsof the FPA detectors were measured and analyzed.The results showed that the signaland noise increased with the integral time, and the average peak responsivity andaverage peak detectivity were0.56A/W and1.20×1012cm·Hz1/2/W respectively, atthe integrated time of3ms.And then the substrate removal was achieved with thecombination of CMP and wet chemical etching.The response spectrum of the FPAdetector covered the wavelength band of0.5-1.7μm, and the sinal and noiseincreased.The average peak responsivity and average peak detectivity were0.70A/Wand1.48×1012cm·Hz1/2/W respectively, at the integrated time of3ms. |
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