A Study Of Photocurrents Of Terahertz Quantum-Well Photodetectors

Terahertz (THz) detectors have been a research subject of growing interest both theoretically and experimentally. Solid-state THz quantum-well photodetectors (THz QWIP) have been widely investigated due to their advantages such as fast responsivity, small size, ease of integration, and mature fabrication technology. Here we study theoretically the photocurrents of THz QWIP and compare the theoretical result with the experimental one. This work is valuable for the device design and for improving the performance of THz QWIP. The contents and main conclusions are listed as follows:1. Some important characteristics of THz QWIP, including photocurrent spectrum, dark current, detector responsivity, and background-limited infrared performance (blip) temperature, are discussed respectively. Increasing barrier thickness is found to be an efficient method to reduce the dark current and to enable blip operation.2. The energy structure of THz QWIP has been studied by using the self-consistent plane-wave numerical approach. The proposed approach is based on the plane-wave expansion of the Schrodinger equation and the Poisson equation over the reciprocal-lattice vectors. A GaAs/AlGaAs THz QWIP is investigated. The energy dispersion of the first six subbands, wave functions, and the density of states are calculated. In calculation we can make sure the convergence by increasing the number of plane waves. It is found that the theoretical results are in good agreement with the experimental ones.3. The influence of the scattering processes of the electrons in the continuum states on the shapes of the photocurrent spectra of THz QWIP are simulated by considering the effects of electron-phonon and electron-alloy-disorder interactions. We take a simple approximation model to calculate the absorption coefficient and obtain the photocurrent spectra which agree with experimental results qualitatively. It is indicated that although our model is simple, it includes the influence of the scattering processes reasonably. The wider photocurrent peak and the asymmetric lineshape of the photocurrent spectrum are also discussed.