Study Of Characteristics Of Surface Photovoltage Of Ⅲ-Ⅴ Photocathode Material With Multi-layer Structures

The theoretical analysis and measuring technique of characteristics of surface photovoltage of Ⅲ-Ⅴ photocathode material with multi-layer structures own important application prospects in fields such as photoelectronic detection,photoelectronic imaging,microelectronics and electron sources.Comprehensive performance non-destructive evaluation of Ⅲ-Ⅴ photocathode material with multi-layer structures before activation based on characteristics of surface photovoltage has been carried out in this thesis.By combining the performance parameters obtained by fitting the experimental data based on the theoretical models of quantum efficiency and surface photovoltage,a closed-loop system of the evaluation of Ⅲ-Ⅴ photocathodes material was established,which provides a better evaluation means for the research of Ⅲ-Ⅴ photocathodes.The main work and ininovations include the following:First,a new device for surface photovoltage measurement within the spectral range of200～1700nm of Ⅲ-Ⅴ photocathode material with multi-layer structures including transmission-mode Ga As,reflective-mode Ga N and transmission-mode Ga Al N is developed.Based on the effects of different experimental conditions on the surface photovoltage,172 Hz and 1 k Hz were used as the optical modulation frequency for the testing of Ga As and Ga N.Secondly,the theoretical model for the surface photovoltage in the transmission-mode Ga As photocathode material with the structure of Ga As/Ga Al As/Ga As/Ga Al As/Ga As is presented.Based on the theoretical model,a method for calculating the performance parameters of the transmission-mode Ga As photocathode material is proposed.The minority carrier diffusion lengths of the active layer（2.0μm,2.1μm and 2.1μm,respectively）and the recombination rates of the active layer/buffer layer interface(1.7×10¹⁰μm/s,1.2×10¹⁰μm/s and 1.0×10¹⁰μm/s,respectively)of the transmission-mode Ga As photocathode materials with different Al composition in the buffer layer were obtained.Then,the generation mechanism of surface photovoltage has been determined and the theoretical model for the surface photovoltage has been derived in the reflection-mode Ga N photocathode materials with the structure of Ga N/Ga N/Al₂O₃ based on the properites and the energy band structures of materials.The minority carrier diffusion lengths of the active layer（180 nm and 290 nm,respectively）in the reflective-mode Ga N photocathode materials with uniform doping and delta doping have been obtained by the fitting calculation.In consideration of the influence of the built-in electric field on the transport of photogenerated carriers,the theoretical model for the surface photovoltage of the transmission-mode Ga Al N photocathode material with the structure of Ga Al N/Ga Al N/Al N/Al₂O₃ is derived based on the one-dimensional steady-state continuity equation.The minority carrier diffusion lengths（65nm,85 nm and 90 nm,respectively）of the transmission-mode Ga Al N photocathode materials with different Al composition in the active layer were obtained by the fitting calculation.Finally,a series of transmission-mode Ga As photocathodes,reflective-mode Ga N photocathodes and transmission-mode Ga Al N photocathodes were activated and the performance parameters were obtained by fitting the experimental data based on the theoretical models of quantum efficiency.The good agreement between the calculation results based on the theoretical model of surface photovoltage and quantum efficiency validates the feasibility and validity of the method for calculating the performance parameters of Ⅲ-Ⅴ photocathode material with multi-layer structures based on surface photovoltage.