GaAs光电阴极表面电子逸出概率与波长关系的研究

GaAs光电阴极量子效率公式中用到的表面电子逸出概率,在阴极工作波段范围内通常视为与入射光子波长无关的常数。应用该结论对反射式GaAs光电阴极激活实验结果进行了拟合分析。实验采用分子束外延GaAs材料,外延发射层厚度为1.6μm、掺杂浓度为1×1019cm-3,分析结果显示理论曲线与实验曲线存在偏差,而在激活台内阴极灵敏度下降后的光谱响应曲线拟合结果偏差更大。这种偏差是由于表面电子逸出概率对入射光子波长的依赖关系造成的,并非通常认为的与波长无关。经过光谱响应曲线的拟合分析得出,反射式阴极表面电子逸出概率与入射光子波长之间近似满足指数关系,两者通过表面势垒因子相联系。高、低温激活后阴极表面势垒因子分别为3.53和1.36。

Study of Relation between Surface Electron Escape Probability of GaAs Photocathode and Incident Photon Wavelength

Surface electron escape probability (P) in quantum efficiency formula of GaAs photocathode commonly is taken for a constant independent of incident photon wavelength (λ) within photocathode working wave band. Quantum efficiency formula is applied in data fitting of spectral response curves of reflectionmode GaAs photocathode grown by molecular beam epitaxy, in which the epitaxial layer thickness is 1.6 μm, and doping concentration is 1×1019 cm-3. Data fitting results show that theoretical curves cannot tally with experimental curves completely, especially with declined spectral response curves of photocathode in activation chamber. This deviation is caused by the relation of P and λ, and P is not a constant independent of λ. Based on the data fitting analysis of spectral response curves, it is found that the relation of P and λ for reflection-mode photocathode approximately satisfies exponential function, and P connects with λ through surface potential barrier factor (k). Photocathode surface potential barrier factors after high- and low-temperature activation process are 3.53 and 1.36 respectively.