Performance Optimization Of Resonant Cavity Enhanced N-GaAs Homojunction Far-infrared Detectors

This paper concentrates on the performance optimization of resonant cavity n-GaAs FIR HIWIP detector. The FIR detector of semiconductor becomes more and more important in the field of astronomy physics. Therefore, it is very meaningful to study resonant cavity n-GaAs FIR HIWIP detector.Firstly, we introduce the experimental instrumentals commonly used in the infrared detector, such as Fourier Transform Infrared Spectrometer, Keithely 2400 Series Source Meter. Then, the theory method-Fresnel matrix method is interpreted, which is used to study the detector. The reflectance and transmission spectrum obtained by the theory method coincides well with the experimental result, suggesting the validity of the theory method. After that, we carry out the rudimental introduction to the HIWIP detector, from which we conclude that the quantum efficiency of the HIWIP detector is to low to satisfy the demand of the practical application. Therefore, it is urgently needed to obtain higher quantum efficiency.For n-GaAs FIR HIWIP detector, we discuss two methods of improving the quantum efficiency: (1) the optimization of the main structure of the detector. (2) applying the appropriate bottom mirror to the detector. After the optimization of the main structure, the highest quantum efficiency is 4.9%, two times higher than the detector before optimization. Then we discuss and compare the two kinds of the designs of the bottom mirror: GaAs bottom mirror and Gold bottom mirror. GaAs bottom mirror is composed of the bottom contact layer and one period of undoped/doped GaAs layers lying below. After optimizing the bottom mirror, the quantum efficiency is 13.2% that is about two times higher than that of the detector (4.9%) without a bottom mirror. Gold bottom mirror consists of a bottom contact layer, an undoped GaAs layer, and a gold layer. The resulting quantum efficiency of the RCE detector with gold mirror is 18.8%, which is larger than those of the p-GaAs and Si HIWIP FIR detectors that were ever reported. The results show that both bottom mirrors enhance the quantum efficiency significantly and the gold mirror seems to be a better choice if not considering the technical difficulty.In order to further improve the quantum efficiency, preliminary study of the top mirror is also conducted. The top mirror shows a satisfactory effect under the condition that the reflectivity of the bottom mirror is high enough. The result is useful to the next mission about the design of the top mirror. In addition, from the reflectance spectrum of GaAs HIWIP detector, we find that most of the incident light is not absorbed by the absorption layer of the detector due to the reflection's loss, thus decreasing the absorption probability and quantum efficiency. To obtain low reflectivity, the antire- -flection layer with pyramid structure is roughly discussed. Then we observe that the antireflection is useful to decrease the reflectivity of GaAs substrate. Therefore, the next job is to apply the antireflection layer with pyramid structure on the n-GaAs HIWIP detector.This work is supported in part by the Natural Science Foundation of China under Contract Nos. 10774100 and 10304010 and the Minister of Education of PCSIRT (Contract No. IRT 0524).