Resonant cavity enhanced (RCE) techniques for increasing the efficiency of quantum well photodetectors

In this dissertation, a novel resonant cavity enhanced (RCE) photodetectors for enhanced quantum efficiency (QE) is studied. By utilizing a resonant cavity around the active region, RCE photodetectors enable the photons to make multiple passes across the active region, improving the probability of absorption. This feature also makes the detector very sensitive to the incident wavelength and the incident angle. Thus several numerical techniques such as a finite difference time domain (FDTD) method as well as a transfer matrix method (TMM) have been developed under this work, and the RCE concept has been applied to novel device structures, including the quantum well infrared photodetectors (QWIP) for long-wavelength applications. The key advantage of using the FDTD method is that it accurately captures the energy distribution inside the cavity as a function of time. This build-up time is an important factor in RCE photodetectors designed for high-speed operations.; As a step towards FDTD simulation, a temperature-dependent Sellmeier equation for AlxGa1-xAs compounds has been derived. Since QWIP and corrugated QWIP (C-QWIP) typically operate at cryogenic temperatures, it is important to know their refractive indices at these low temperatures. This refractive index model is applied to the analysis of the device structures.; Both grating-coupled QWIP and C-QWIP are investigated and simulated using the FDTD method. Although these structures have been proven to have high reliability and ease of manufacture in infrared applications, their low quantum efficiencies make them less favorable compared to mercury cadmium telluride (HgCdTe) detectors, which have nearly 100% QE. In order to alleviate some of these problems, a novel RCE approach is proposed for the QWIP and C-QWIP structures to enhance their QE and to make them more attractive. These structures are named RCE-QWIP and RCE-CQWIP, respectively. QE is even further enhanced in the RCE-CQWIP by using a novel implementation that includes a form birefringence layer to overcome the polarization selection rule in quantum well sub-band transitions. This structure allows part of the remaining half of the photons to be absorbed, significantly increasing the QE. Dependence of QE on the angle of incidence in both cases is also discussed.