Preparation of negative electron affinity gallium nitride photocathode

Abstract

Negative electron affinity (NEA) Gallium Nitride (GaN) photocathode is an ideal new kind of UV photocathode. NEA GaN photocathode is widely used in such fields as high-performance ultraviolet photoelectric detector, electron beam lithography etc. The preparation of negative electron affinity gallium nitride photocathode relates to the growth technology, the cleaning method, the activation method and the evaluation of photocathode. The mainstream growth technology of GaN photocathode such as metal organic chemistry vapor phase deposits technology, molecule beam epitaxial technology and halide vapor phase epitaxial technology were discussed. The chemical cleaning method and the heat cleaning method for GaN photocathode were given in detail. After the chemical cleaning, the atom clean surface was gotten by a 700 °C heat about 20 minutes in the vacuum system. The activation of GaN photocathode can be realized with only Cs or with Cs/O alternately. Using the activation and evaluation system for NEA photocathode, the photocurrent curve during Cs activation process for GaN photocathode was gotten. The evaluation of photocathode can be done by measuring the quantum efficiency. Employing the UV spectral response measurement instrument, the spectral response and quantum efficiency of NEA GaN photocathode were measured. The measured quantum efficiency of reflection-mode NEA GaN photocathode reached up to 37% at 230 nm.