Study On Passivation Mechanism Of Extended Wavelength InGaAs Detectors

The short-wave infrared band(1?2.5?m)is an important atmospheric transmission window.The substances on the earth exhibit unique spectral characteristics by reflecting the sunlight in the environment,such as the hydroxide roots contained in rocks and minerals,water in crops,CO₂,NH₃,H₂S,N₂O,etc.in the atmosphere.Many characteristic spectra are concentrated in the range of 2.0?2.5?m.With the increase of the In composition,the rear cut-off wavelength of the extended wavelength InGaAs detector extends to the long wave,and there is a significant application demand for short-wave infrared aerospace applications.Therefore,extended-wavelength InGaAs detectors have become one of the best choices for miniaturized,low-cost and highly reliable short-wave infrared detection systems.In this paper,aiming at the application requirements of high-performance mesa-type extended wavelength InGaAs detectors,in order to obtain low dark current density and high detectivity mesa-type extended-wavelength InGaAs detectors,the passivation mechanism of mesa-type extended-wavelength InGaAs detectors is investigated.The main research contents and innovations involved are as follows:1.A low-stress SiN_x passivation film process method is proposed and realized.A low-stress SiN_x dielectric film deposition process is proposed.The film preparation process parameters that affect the stress state of the SiN_x film are analyzed.The flatness,stress distribution,thermal stability and passivation effect of the SiN_x film are studied,and the optimized SiN_x film deposition parameters is obtained.The film deposition parameters reduce the bowing of the 2-inch wafer caused by the SiN_x passivation film from more than 40?m to less than 10?m.In addition,the low-stress SiN_x passivation film has been successfully applied to the flatness control of extended wavelength InGaAs chips in a number of aerospace engineering projects.2.Combined with the above-mentioned low-stress SiN_x film,the SiN_x/Al₂O₃bilayer is introduced as a new passivation process method for the passivation film.In the extended wavelength InGaAs detector,the bilayer passivation method combining the Al₂O₃ film deposited by the atomic layer and the low-stress SiN_x film is introduced,which effectively reduces the generation and recombination current generated on the side surface of the mesa-type In_0.74Ga_0.26As detector.What's more,the dark current density is reduced by an order of magnitude(200 K,-0.01 V).In addition,the SiN_x/Al₂O₃ bilayer effectively reduces the 1/f noise of the mesa-type In_0.74Ga_0.26As detector,especially at low temperatures.3.The surface and interface properties of SiN_x/In_0.74Al_0.26As and Al₂O₃/In_0.74Al_0.26As were compared and studied.The dark current suppression mechanism of the composite passivation film on the extended wavelength InGaAs device is clarified.Using SEM,TEM,XPS and other microscopic characterization methods,the surface and interface characteristics of SiN_x/In_0.74Al_0.26As and Al₂O₃/In_0.74Al_0.26As were studied.The results show that the Al₂O₃/In_0.74Al_0.26As interface is clearer,and the transition zone is only 3 nm.Treated by hydrofluoric acid buffer and combined with Al₂O₃ deposited by atomic layer deposition can effectively inhibit In₂O₃ at the interface between the dielectric film and In_0.74Al_0.26A layer.Designed and developed MIS devices with different passivation films as dielectric films.The interface state density of the three passivation films was extracted.It was found that the fast interface state density of Al₂O₃/In_0.74Al_0.26As was about 1.83×10¹²cm^-2·eV^-1,which was 1ower by 1 order of magnitude than that of SiN_x/In_0.74Al_0.26As.4.The dark current characteristics of In_0.74Ga_0.26As detectors with or without hydrofluoric acid buffer treatment and different test temperatures were compared and analyzed.The extended wavelength InGaAs detector treated with hydrofluoric acid buffer has a smaller average dark current and better uniformity.According to the dark current model of the detector,the dark current of In_0.74Ga_0.26As detectors with different photosensitive element areas were fitted with variable temperature.At room temperature,the dark current of the detector was mainly composed of diffusion current,generation and recombination current and shunt current.As the temperature decreases,the ratio of diffusion current to the total dark current decreases,and the ratio of the trap-assisted tunneling current to the total dark current increase.5.The new SiN_x/Al₂O₃ passivation method was successfully applied to the development of a 1024×32-element mesa-type InGaAs detector,which verified the passivation effect of the SiN_x/Al₂O₃ passivation film on high-density and long-line extended wavelength InGaAs detector.At 200 K operating temperature,when the integration time is 11.2 ms,the^*of the focal plane detector is 2.24×10¹² cm Hz^1/2/W.The noise of the focal plane detector is dominated by the coupling noise between the readout circuit and the photosensitive chip.