Measurement and analysis of surface photovoltage of GaAlN material with multi-layer structrues

Abstract

Three kinds of transmission type GaAlN photocathode materials with GaAlN activation layer/GaAlN absorber layer/AlN buffer layer/Al2O3 substrate layer multi-layer structures with different Al compositions were designed and grown. The thickness of the GaAlN activation layer, the GaAlN absorber layer and the AlN buffers layer of the three samples were 40 nm, 20 nm and 100 nm respectively. The Al fraction of the GaAlN activation layer of the three samples were 0.48, 0.37 and 0.25 respectively, and the Al fraction of GaAlN absorber layer were 0.8, 0.68 and 0.3 respectively. An ultraviolet waveband surface photovoltage testing device was developed for the measurement of the characteristics of surface photovoltage of the three GaAlN photocathode materials. The surface photovoltage amplitude curves of the three samples were basically the same under the two cases of frontal and reverse incidence, and the surface photovoltage signals obtained by the two different light incidence methods were differentiated, and the extreme points of the differentiation curves were obtained near the positions of 4.47 eV, 4.21 eV and 3.92 eV respectively, which correspond to the forbidden band width of the GaAlN material in the activation layer of the three samples. Comparing the surface photovoltage curves before activation with the spectral response curves after activation of two samples, it is found that the surface photovoltage curves before activation and the spectral response curves after activation are highly consistent in characteristics of spectral response and cut-off, which proves the effectiveness of surface photovoltage in the evaluation of characteristics of the spectral response of the GaAlN photocathode materials with multi-layer structures.