Research On Graded Components Al_xGa_1-xAs/GaAs Photoemission Materials

In recent years, with the fast development of the biomedical technology, the environment monitoring, the space exploration and other fields, the photoelectric detectors with higher spectral response and sensitivity were required. The detected optical signals in these fields are generally very weak, such as biological fluorescence, uv radiation, and the spectral range varies from near infrared, visible light to ultraviolet. GaAs photoemission materials act as one of the highest efficient materials for detection in those field. Therefore, in order to further improving the sensitivity of the GaAs-based photoemission detection, and expanding the range of the detected spectrum, the researchers have carried out a lot of investigations all around the world. In this work, we present a graded composition AlxGa1-xAs/GaAs photoemission materials, in which a built-in electric field can be induced by the graded composition AlxGa1-xAs layer. This structure can greatly improve the quantum efficiency of photocathodes.In this paper, we establish a photoemission model for graded composition AlxGa1-xAs /GaAs photocathodes based on the finite volume method. The model is used to analyze the effects of the AlxGa1-xAs /GaAs material parameters on the quantum efficiency and the resolution for photocathodes. The simulation results are used to optimize the structure of AlxGa1-xAs photoemission material. Through the simulation of graded composition AlxGa1-xAs /GaAs photoemission film materials and combining with experimental results, we obtain the optimal Al composition and thickness of material structure, in which the photocathodes can achieve the highest quantum efficiency and resolution. According to the simulation of graded composition AlxGa1-xAs /GaAs nanowire cathodes, we obtain the optimal GaAs nanowires length and the Al composition range of nanowire cathodes.