Design of bottom mirrors for resonant cavity enhanced GaAs homojunction far-infrared detectors

The design of bottom mirrors for resonant cavity enhanced (RCE) GaAs homojunction far-infrared (FIR) detectors has been investigated in the framework of three possible projects. The results show that neither the bottom contact layer of the detector itself nor the distributed Bragg reflector, which has been widely employed in near- and mid-infrared detectors, can perform well as bottom mirrors for FIR detectors. A new kind of bottom mirrors based on undoped/doped GaAs layers is proposed and optimized. Though the absorption cannot be neglected, the bottom mirror shows a satisfactory effect. The resulting absorption probability (as well as the quantum efficiency) in the detector cavity for this kind of RCE p-GaAs FIR detector is three times of the normal p-GaAs homojunction FIR detector demonstrated experimentally. This kind of bottom mirror design opens a new way to increase the quantum efficiency in homojunction FIR detectors.