Wet etching of AlGaN/GaN photocathode grown by MOCVD

The AlGaN/GaN with thin GaN surface was grown by metalorganic chemical vapor deposition (MOCVD). One of two AlGaN/GaN photocathode samples was etched by molten KOH about 40s, and its reflectivity and transmittance are tested. The thickness of AlGaN and GaN layers are fitted by the matrix formula for thin film optics, in which the GaN thickness of them are 7nm and 2.5nm respectively, and got the etch speed of GaN. Then the etched and original AlGaN/GaN photocathode samples are activated by Cs/O in the same way. The spectral response and the result of simulation show that the cut-off wavelength of the etched AlGaN/GaN deviate to the short-wave, and the quantum efficiency decline with the GaN thickness decrease.