Detection wavelengths and photocurrents of very long wavelength quantum-well infrared photodetectors

Journal article, 2005

Based on detailed studies of the energy band structure and the optical transitions in very long wavelength (>14 μm) GaAs/AlGaAs quantum-well (QW) infrared photodetectors (QWIPs), we have built a practical QWIP model. We study the factors that determine photogenerated carriers and response wavelengths of photocurrents of very long wavelength QWIPs. The material structures of QWIPs are first characterized by the photoluminescence measurements (PL) at room temperature and 77 K respectively. We have found and confirmed a distinctive difference between photocurrent of QWIPs with only one confined state in the quantum well (QW) and those binding two confined states, which resulted in different dependence of detection wavelength on the quantum well width. Also, we have investigated the dependence of response wavelength on several other parameters for very long wavelength QWIPs, such as barrier width and Al mole fraction. By calculating the density of photogenerated carriers in the continuum above the energy barriers using the PL calibrated QWIP structures, we have demonstrated that due to the high sample quality, the photocarriers can be either in miniband states (Bloch states in the multiple quantum wells), or they transport from one quantum well to the next in the form of propagating waves. We have further calculated the densities of photocarriers in the QWIPs reported in the literature. It is shown that the Bloch wave boundary conditions are appropriate for QWIPs with narrow QWs, whereas propagating wave boundary conditions are appropriate for wide QWs.