Study On Surface And Interface Characteristics Of Extended Wavelength InGaAs Infrared Detector

Ⅲ-Ⅴ family In Ga As detectors show a clear advantage in shortwave infrared band due to their high operating temperature, high detectivity, anti-radiation, etc. With further demand in space remote sensing and imaging applications, advanced In Ga As detector with larger array, higher performance and lower cost becomes the focus of future development. For extended wavelength In Ga As detectors(> 1.7μm), due to lattice mismatching between absorbing layer and In P or Ga As substrate, In Ga As absorbing layer exists a lot of dislocations and defects such that the detectors withstand too large dark current. It is extremely urgent to reduce the noise and improve the detectivity of detectors by lowering dark current. In this paper, inductively coupled plasma chemical vapor deposition(ICPCVD) passivation process with the advantages of high-quality, low damage, good coverage was researched on the mesa structure extended wavelength In Ga As detectors, and some certain results were achieved.Surface passivation treatment process with the BHF solution treatment + N2 plasma cleaning + ICPCVD deposition of dielectric films was studied, and Si Nx and Si O2 thin films were deposited by using Si H4/N2 and Si H4/N2 O reactants, respectively. Orthogonal experiment method was designed to study the effects of ICP power, RF power, chamber pressure and other growth parameters on the film properties of Si Nx and Si O2 thin films. At last, optimized film growth conditions with compact, good uniformity, good surface morphology and thermal stability characteristics were obtained for Si Nx and Si O2 thin films. The ICPCVD process Si Nx films were analyzed by X-ray photoelectron spectroscopy(XPS). The observed Si 2p peak was decomposed into five peaks by using the Gaussian method, and the integrated peak area ratio of Si0, Si+1, Si+2, Si+3 and Si+4 was 5.0%, 4.8%, 18.2%, 36.4% and 35.6%, respectively. Compared to the XPS analysis of the Si Nx films deposited by optimized PECVD technology in other reference, the Si Nx films deposited by ICPCVD showed obviously better quality.Based on extended wavelength InGa As epitaxial materials, MIS capacitors were fabricated by utilizing Si Nx films which were deposited by PECVD process and ICPCVD process respectively. Fast(slow) interface state density, fixed charge density, the doping concentration of the substrate and film resistivity were calculated by high frequency C-V curves for different processes based MIS capacitors.Compared with the PECVD process MIS capacitors, the slow interface state density of ICPCVD process MIS capacitors was reduced from 3.61×1012cm-2 to 1.74×1012cm-2, but fast interface state density, the fixed charge density and film resistivity did not show a significant difference.N on p structure 8×1 linear arrays extended wavelength In0.78Ga0.22 As detectors with cutoff wavelength of 2.4μm were researched. Deep mesa was achieved for detectors by ICP etching process, and Si Nx films deposited by ICPCVD were applied as passivation films. Before films deposition, the material surface is rinsed in 3: 6: 10 hydrofluoric acid buffer solution(BHF) followed by ICP excited N2 plasma pre-cleaning. The test results indicated that perimeter-dependent leakage current was negligible, illustrating the good surface passivation effect, and the devices showed better dark current characteristics that the dark current densities were 94.2n A/cm2 and 5.5×10-4A/cm2 at 200 K and 300 K, respectively. N on p structure 8×1 linear arrays extended wavelength In0.83Ga0.17 As detectors with cutoff wavelength of 2.6μm were researched. Two kinds of material structures with absorbing layer doping concentrations of 1×1016cm-3 and 3×1016cm-3 were used, and PECVD and highrate mode ICPCVD passivation processes were applied. The test results indicated that the total and perimeter-dependent leakage currents of ICPCVD process detectors were lower. The analysis of activation energy showed the major components of the area-dependent leakage current were diffusion and generation-recombination current. At reverse bias of 0.1-0.5V and temperature of 200K-300 K, the perimeter-dependent leakage current is dominated by surface recombination current mechanism for ICPCVD, while it is dominated by ohmic current and surface recombination current mechanisms for PECVD.The impacts of N2/Si H4 flow ratio and substrate temperature on Si Nx films deposition rate, BHF wet etch rate, adhesion, elemental composition and annealed condition were studied. MIS capacitors were fabricated by applying different passivation process, Si Nx/In Ga As interface characteristics were studied with Si Nx films deposited by original process(experimental 3) and higher substrate temperature condition process(experimental 7). Interface state density, the fixed charge density and slow interface defects of experimental 7 MIS capacitors was reduced compared with the experimental 3 MIS capacitors, and the capacitance loss of experimental 7 MIS capacitors was smaller. P on n structure extended wavelength In Ga As detectors were fabricated by varied passivation process. Compared with the original process, the dark current of experimental 4 photodiodes which increased the N2/Si H4 ratio decreased effectively, while the dark current of experimental 1 photodiodes which decreased the N2/Si H4 ratio process increased, and the dark current of experimental 7 photodiodes which increased the substrate temperature decreased slightly. For experimental 4 photodiodes, the quality of Si Nx passivation films became better with the N/Si element ratios closer to 4/3 by increasing the N2/Si H4 flow ratio, resulting in better passivation effect. For experimental 7 photodiodes, the interface characteristics between Si Nx passivation films and extended wavelength In Ga As epitaxial material were improved by raising the substrate temperature, also resulting in better passivation effect.In summary, firstly, grown parameters of dielectric films based on inductively coupled plasma chemical vapor deposition(ICPCVD) were researched, secondly, the interface characteristics between passivation films produced by different processes and extended wavelength In Ga As epitaxial material were analyzed, thirdly, the passivation film grown by ICPCVD was applied to extended wavelength In Ga As detectors, finally, further improving of the ICPCVD passivation process was studied and dark current of extended wavelength In Ga As photodiode was reduced effectively. These works have some certain values for ICPCVD thin films deposition process and certain significance for improvement of interface characteristics and passivation technology of semiconductor devices.