A Study Of Terahertz Quantum-Well Detector

Recently, there has been an increasing interest in terahertz (THz) detectors with the rapid development of terahertz technology. After extending the wavelength coverage of quantum-well infrared photodetectors into the THz region, we get a new type of THz detector, THz quantum-well detector. This thesis presents an investigation in optimizing the design and improving the characteristics of THz quantum-well detector. The main contents and conclusions are as follows:1. According to the principle of having the first excited state in resonance with the top of the barrier, optimum quantum-well parameters are calculated. Some important characteristics, including detector responsivity, dark current, are studied respectively. A few suggestions are also presented in order to improve the performance of the detector.2. The reststrahlen region of GaAs, caused by the coupling of electromagnetic radiation and transverse optical phonons around the origin of Brillouin zone, is studied in this thesis. The real refractive index n(ω) and the extinction coefficient k(ω) is calculated using the " single oscillator" model. Some improvements are made on the usually used expression of detector responsivity, taking into account the strong absorption by the optical phonon of GaAs. After comparing the theoretical result with the experimental one, it is found that the theoretical result is in good agreement with experiment, which indicates the improvements are reasonable.3. A magnetically tunable THz quantum-well detector made in diluted semiconductor ZnSe/(Zn,Cd,Mn)Se is investigated in this thesis. The electronic conduction band and the absorption spectrum are calculated within the effective mass approximation. It is found that the intersubband transition energy increases with magnetic field for spin-down transitions and decreases for spin-down transition until the sp - d exchange begins to saturate under stronger magnetic field, the absorption peak for the spin-down transition has shifted from 44 meV to 56 meV, and the height of the peak has increased by about 1.5 times as the applied magnetic field increases from 0 to 9 T when the barriers are 0.08 eV. The excellent performance and large tunable region offer a promising approach to design a magnetically tunable THz QWIP with DMS materials.