To improve the quantum efficiency of the extended blue varied-doping Ga0.37Al0.63As photocathode, different cleaning methods for oxide and carbon on the surface of the Ga0.37Al0.63As photocathode were investigated. The surface structure and atomic compositions of the Ga0.37Al0.63As photocathode were measured by X-ray photoelectron spectroscopy and Ar+ ion sputtering. After preparation and activation of the Ga0.37Al0.63As photocathode in an ultra-high vacuum system, the spectral response curves and quantum efficiency curves were measured, and then, curve fitting and analysis were performed. The experimental results showed that in regard to surface chemical cleaning of the Ga0.37Al0.63As samples, it was difficult to effectively remove the oxide with only the H2SO4: H2O2: H2O (4:1:100) solution, while carbon could not be removed with the HCl: H2O (1: 3) solution alone. A two-step chemical cleaning method with the H2SO4: H2O2: H2O (4:1:100) solution and HCl: H2O (1:3) solution could effectively remove the oxide as well as the carbon. After cleaning, the quantum efficiency was increased from 18% to 27% at 532 nm and the electron escape probability was increased from 0.51 to 0.71. (C) 2017 Elsevier B.V. All rights reserved.