发射层厚度对反射式GaAs光电阴极性能的影响

Influence of Active-Layer Thickness on Reflection-mode GaAs Photocathode

通过求解扩散方程,推导了含有后界面复合速率的反射式GaAs光电阴极量子效率公式,并利用MBE在GaAs(100)衬底上外延生长了发射层厚度分别为1.6μm、2.0μm和2.6μm,掺杂浓度为1×1019cm-3的三个反射式GaAs阴极样品,进行了激活实验.实验结果显示:随着发射层厚度的增加,阴极的长波量子效率和灵敏度都有所提高,而这种提高与阴极电子扩散长度的增长有关.同时,理论仿真研究发现,当后界面复合速率小于或等于105cm/s时,阴极发射层有一个最佳厚度,此时阴极灵敏度最高.后界面复合速率对阴极灵敏度在发射层厚度较小时影响较大,而随着厚度的增大阴极灵敏度最终趋于稳定.

The quantum-efficiency equation of the reflection-mode GaAs photocathode with back-interface recombination velocity is solved from the diffusion equation. Three reflection-mode cathode materials are grown on a GaAs wafer （100） by molecular beam epitaxy,the active-layer thickness of which are 1.6μm, 2.0 μm and 2.6 μm, respectively,and the doping concentration is 1×10^19cm^-3. The results of activation experiments show that the quantum efficiency of long-wavelength photons and the integral sensitivity for cathodes increase with the increase in active-layer thickness, which is due to the increase of electron diffusion length. Through the theoretical simulation, it is found, as the back-interface recombination velocity is less than or equal to 105cm/s, the active-layer thickness has an optimum value in which the cathodes achieve the maximum sensitivity. The influence of recombination velocity on cathodes with a small active-layer thickness is great ,and with the increase in thickness, the sensitivity of cathodes finally tends to a stable value.