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Experimental results showing room temperature normal incidence mid-infrared detection by AlGaN/GaN quantum well infrared photodetectors are presented. Designed structures have intersubband transitions corresponding to wavelengths in the region of 3 and 4 µm, where strong absorption in a sapphire substrate dominates. The intersubband spectra, therefore, were characterized by electronic Raman scattering and infrared photocurrent spectroscopy. The absorption spectra agree well with theoretical predictions. Details of device fabrication are presented with sensitivity estimates for the devices.

Analysis of carrier transport in cascaded GaAs/AlGaAs, p-Si/SiGe and GaN/AlGaN terahertz structures is performed using self-consistent rate equations with kinetic energy-balance simulations. The electron transport in n-type structures is simulated using standard envelope function and nonparabolic effective mass approximations with all relevant electron–electron and electron–optical phonon scattering. In the case of GaAs-based structures the model is extended to include ionized impurity and interface roughness scattering as well. The hole subband structure in the p-type device is calculated using the 6 × 6 k p model, and then used to find carrier relaxation rates due to the alloy disorder, acoustic and optical phonon scattering, as well as hole–hole scattering. The simulation accounts for the in-plane k-space anisotropy of both the hole subband structure and the scattering rates. Results are presented for the original GaAs/AlGaAs THz quantum cascade laser and prototypes of GaN/AlGaN and Si/SiGe THz quantum cascade structures.