Study On High Sensitivity Planar InGaAs Short Wavelength Infrared Detector

InxGa_1-xAs is an excellent material which can be used in the detection of short wavelength infrared waveband, and has important application value in the field of space remote sensing. According to the requirement of high sensitivity detection, the key process and the related physical mechanism of the planar InxGa_1-xAs detector were studied in this paper. Firstly, the temperature characteristics of ohmic contact between p-type electrode metal and semiconductor were studied for the lattice matched and extended-wavelength In Ga As detector. Secondly, the influence, caused by the heat treatment in the vacuum environment, on the passivation properties of Si Nx film was analyzed, and the thermal conditions to activate diffusion impurity was optimized. The device verification was carried out by the perimeter area ratio devices, 32×32 element and 5¹²Ã—256 element detector, to analyze the influence of the thermal activation on the dark current, detectivity and uniformity. And the high performance 1024×¹²8 element In Ga As focal plane arrays were fabricated by the optimized process. Finally, the diffusion process parameters of the extended wavelength In Ga As detector were optimized, and device verification was carried out. The minority carrier diffusion length was measured by LBIC. The dark current mechanism of planar extended wavelength In Ga As detector was analyzed.The temperature characteristics of contact between electrode metal and semiconductor were studied for the lattice matched In Ga As detector. It was found that the room-temperature special contact resistance was 3.84×10^-4 ??cm² after annealed at 480?C with 30 s, and as the temperature decreased, the special contact resistance increased while the contact performance decreases. It is proved that the electron transfer mechanism on the contact interface was mainly the thermal field emission. Tunneling factor, the barrier height and the difference between the Fermi level and the valence band were 0.44 e V, 0.13 e V and 0.59 e V, respectively. For the planar extended wavelength In Ga As detector, the excellent Au/p-In0.82Al0.18 As contact was formed after annealing at 480?C for 15 s and 450?C for 15 s, and the specific contact resistance were 6.07×10^-5 ?·cm² and 1.28×10^-4 ?·cm² at room temperature, respectively. It was found that the specific contact resistance increases with the increase of temperature with the power index, which was in contradiction with the traditional metal-semiconductor theory. TEM analysis showed that the abnormal electrical phenomenon was likely to be caused by the metal inclusions on the interface.The effect of vacuum heat treatment on passivation of Si Nx films was studied by PL spectroscopy. The PL peak intensity of sample was significantly improved after heat treatment in vacuum environment. Test structure devices were fabricated to make research. The device, in which Si Nx film was annealed in vacuum environment, hads lower dark current, and the dark current density was 10 n A/cm² at-0.1V. The surface leakage model was established to study the leakage mechanism. The activation optimization of impurity Zn and its effect on detector performance were studied, and the optimized heat treatment parameters were obtained. The analysis for test structure devices showed that the dark current of devices was obviously decreased after the activation treatment. The 32×32 element array detector was fabricated by the original and optimized process,and the 5¹²Ã—256 element detector was also prepared by the original process in 2 inch wafer. Through comparative analysis of 32×32 element array detector, the optimized technology was superior to the original process in the dark current density and detectivity. The signal of 5¹²Ã—256 element focal plane arrays fabricated by the original process was abnormal, and SCM analysis showed that there was the anti-type zone in the samples without thermal activation, which might cause photosensitive element collecting no carriers. With the optimized process, 1024×¹²8 In Ga As focal plane arrays was prepared, and the bad-pixel ratio, the non-uniformity and the room-temperature detectivity were 0.46%, 3.8% and 3.07×10¹²cm Hz^1/2/W, respectively.The diffusion behavior of Zn in high In component In0.82Al0.18 As materials was investigated, and the diffusion activation energy of Zn was 1.06 e V, which meant the diffusion was mainly decided by the interstitial mechanism. The effect brought in by Zn diffusion on the hetero-junction interface was studied, and it was found that the reduction of diffusion temperature could suppress the damage to the heterojunction interface, and kept the integrity of super-lattice structure. The photoelectric performance of test structure devices, prepared by different process, was characterized. The light current-voltage curve showed that the PN junction of sample was normal. At room temperature and 200 K, the cutoff wavelengths were 2.56 μm and 2.40μm, respectively, and signal increased approximately linearly with the increase of temperature, and noise decreased with the decreasing of temperature. The detectivity of device diffused at 400 oC has higher detectivity, and the detectivity was about 6.8×1011cm Hz^1/2/W at 200 K.The peak quantum efficiency was more than 80%. By use of LBIC, the minority carrier diffusion length of material in the planar extended wavelength detector was researched. It was found that through the scanning of 980 nm laser, the minority carrier diffusion length displayed a linear relationship with T^1/2 below 260 K. Utilizing the 2.0μm wavelength laser, the uniformity of the photodetector was analyzed, and the minority carrier diffusion length of absorbing layer was obtained, which was 4.91μm at 25 oC and 3.09μm at-35 oC.The effect of surface passivation and diffusion on the dark current of detector was studied. The results showed that the dark current of the planar extended wavelength In Ga As detector was mainly derived from the bulk. Si Nx passivation film had little influence on the dark current of detector, but the diffusion temperature had much more influence on the performance of detector. Compared with the 500 oC, the device diffused at 400 oC had the lower dark current, and the dark current decreased by 1 order of magnitude at 200 K. Dark current analysis showed that the dark current was mainly composed of diffusion current, generation-recombination current and shunt current at room temperature. At 200 K, the main dark current components were generation-recombination current, shunt current and the band trap band tunneling current. However, due to the different diffusion processes, the shunt current and the band trap band tunneling current were quite different, which provided theoretical basis for the improvement of performance for the extended wavelength detector.