Influence of Ga1-xAlxAs buffer layer on the optical properties in NEA GaAs photocathodes

GaAs/Ga<;sub>1-x<;/sub>Al<;sub>x<;/sub>As(0<;x<;1.0) multilayer structure is widely used in photodetector, laser and solar cell. Due to the lattice parameter difference between GaAs and Ga<;sub>1-x<;/sub>Al<;sub>x<;/sub>As is very small(less than 0.15% at 300K), Ga<;sub>1-x<;/sub>Al<;sub>x<;/sub>As as a buffer layer in NEA GaAs photocathodes can improve back surface recombination and provide a good interface properties. GaAlAs/GaAs/Ga<;sub>1-x<;/sub>Al<;sub>x<;/sub>As multilayer structure were epitaxial grown by metal-organic chemical vapor deposition on GaAs substrate. Through a series of selected etching, NEA GaAs photocathodes with Glass/Si<;sub>3<;/sub>N<;sub>4<;/sub>/Ga<;sub>1-x<;/sub>Al<;sub>x<;/sub>As/GaAs configuration are achieved using inverted structure method. This paper investigates the influence of Ga<;sub>1-x<;/sub>Al<;sub>x<;/sub>As buffer layer's thickness and the values of x on the optical properties of NEA GaAs photocathodes. Through the use of thin film optical formula, theoretical reflectance and transmittance of NEA GaAs photocathode samples are derived within a spectral range from 400 nm to 1100 nm. Absorptance of NEA GaAs photocathode can be figured out based on the law of conservation of light energy. Absorptance curves varying with the thickness d show that two samples' absorptance display different variation trend.