Second harmonic generation at the quantum-interference induced transparency in semiconductor quantum wells: The influence of permanent dipole moments

The influence of permanent dipole moments of quantized states on intersubband second harmonic generation based on quantum-interference induced transparency in semiconductor quantum wells is explored using the harmonic balance method. The permanent moments are found to be quite important: they affect the transparency condition, especially at larger pump intensities. Hence, both the conversion efficiency and the optimal interaction path length change significantly when accounting for the permanent moments, and the conversion efficiency is reduced

On the interdiffusion-based quantum cascade laser

Design procedure for the active region of current pumped quantum cascade laser is proposed, so to achieve maximal gain. Starting with an arbitrary smooth potential, a family of isospectral Hamiltonians with predefined energy spectrum is generated using the inverse spectral theory. By varying the relevant control parameter the potential shape is varied, inducing changes in transition dipole moments and electron–phonon scattering times, and the optimal potential which gives the largest gain is thus found. For purpose of realization, a simple step quantum-well structure with just a few layers is then designed so that in the post-growth heating-induced layer interdiffusion, it will acquire a shape as close as possible to the optimal smooth potentia

Dilute magnetic semiconductor quantum-well structures for magnetic field tunable far-infrared/terahertz absorption

The design of ZnCdSe–ZnMnSe-based quantum wells is considered, in order to obtain a large shift of the peak absorption wavelength in the far infrared range, due to a giant Zeeman splitting with magnetic field, while maintaining a reasonably large value of peak absorption. A triple quantum-well structure with a suitable choice of parameters has been found to satisfy such requirements. A maximal tuning range between 14.6 and 34.7 meV is obtained, when the magnetic field varies from zero to 5 T, so the wavelength of the absorbed radiation decreases from 85.2 to 35.7 μm with absorption up to 1.25% at low temperatures. These structures might form the basis for magnetic field tunable photodetectors and quantum cascade lasers in the terahertz range

Optically pumped terahertz laser based on intersubband transitions in a GaN/AlGaN double quantum well

A design for a GaN/AlGaN optically pumped terahertz laser emitting at 34 µm (ΔE~36 meV) is presented. This laser uses a simple three-level scheme where the depopulation of the lower laser level is achieved via resonant longitudinal-optical-phonon emission. The quasibound energies and associated wave functions are calculated with the intrinsic electric field induced by the piezoelectric and the spontaneous polarizations. The structures based on a double quantum well were simulated and the output characteristics extracted using a fully self-consistent rate equation model with all relevant scattering processes included. Both electron-longitudinal-optical phonon and electron-acoustic-phonon interactions were taken into account. The carrier distribution in subbands was assumed to be Fermi–Dirac-like, with electron temperature equal to the lattice temperature, but with different Fermi levels for each subband. A population inversion of 12% for a pumping flux Φ=10(27) cm(–2) s(–1) at room temperature was calculated for the optimized structure. By comparing the calculated modal gain and estimated waveguide and mirror losses the feasibility of laser action up to room temperature is predicted