Design Of A High-efficiency Resonant Cavity Enhanced GaAs Homojunction Far-infrared Detectors

This paper concentrates on the design of a high-efficiency resonant cavity of n-GaAs FIR HIWIP detector. The FIR detector of semiconductor becomes more and more important in many fields such as astronomy physics. Therefore, it is very meaningful to study how to improve and enhance the performance and function of the resonant cavity n-GaAs FIR HIWIP detector.Firstly, we introduce the experimental apparatuses commonly used in studying the infrared detectors, such as Fourier Transform Infrared Spectrometer based on the Fourier Transform Spectroscopy, as well as Keithely 2400 Series Source Meter based on the computer-compatible auto-reading and auto-recording. Then, the theory method of Fresnel matrix method often used in calculating the optical absorption of multi-layers is interpreted, which is applied to study the detector. The reflectance and transmission spectrum obtained by the theory model coincides well with the experimental results, suggesting the validity of the theory model. After that, we carry out the overall introduction to the HIWIP detector, from which we conclude that the quantum efficiency of this kind of detector is still too low to meet the demand of the practical application. Therefore, it is urgently needed to gain higher quantum efficiency of the detector.For n-GaAs FIR HIWIP detector, our previous work discussed two methods of enhancing the quantum efficiency: (1) the optimization of the parameters of main structure of the detector. (2) applying certain appropriate bottom mirror to the detector. After the optimization of the detector main structure, the highest quantum efficiency is 4.9%, two times higher than the detector without optimization. Then based on the optimized main structure, we discuss and compare the two kinds of the bottom mirror: GaAs bottom mirror and Gold bottom mirror. After optimizing the GaAs bottom mirror, the quantum efficiency can reach to 13.2%, a number that is about two times higher than that of the detector (4.9%) without a special bottom mirror. The resulting quantum efficiency of the RCE detector with the optimized Gold bottom mirror is 18.8% (for the reflection of the optimized Gold bottom mirror is much larger), a number much larger than those of the p-GaAs and Si HIWIP FIR detectors which were ever reported. But these numbers of quantum efficiency are still not satisfactory, and there are no specific optimization for top mirrors. So, in this thesis, our work is discussing how to obtain an ideal top mirror for the"half-optimized detector"(composed of the optimized main structure plus the optimized Gold bottom mirror discussed before in this paragraph), to enhance the quantum efficiency another step forward. From the most simple situation, we discuss firstly one single dielectric layer(authentic or equivalent) as the top mirror. We found that no matter what the thickness and refractive index are, it cannot achieve the expected reflectivity and matched phase shift simultaneously, so is unqualified to be the ideal top mirror. Naturally, we turn to a complicated structure that cannot be equivalent to one single layer, i.e. the 2D(two dimensional) periodical reversed pyramidal structure of intrinsic GaAs as the top mirror. When applied to the"half-optimized detector", a series of simulation results show that this structure as the top mirror can achieve the expected reflectivity and matched phase shift simultaneously, making the whole detector's quantum efficiency as high as 29.0%, about 50% higher than 18.8% of the"half-optimized detector". We discuss the reason why this reversed pyramidal structure can be the ideal top mirror in detail, in comparison to the situation of one single layer as the top mirror. Finally, we present a tentative fabrication solution on how to realize such a top mirror of this reversed pyramidal structure. All this content is within chapter 5.In chapter 6, we make some fundamental discussion on the possible problems of the 2D periodical reversed pyramidal structure of intrinsic GaAs. Then we come up with two improved structures and make some simple analysis. We hope all the structures mentioned above can be not only fit for our detector, but also be a useful reference for designing other IR devices.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).