Femtosecond two-color pump-probe experiments in the mid-infrared are performed on intersubband transitions in GaN=Al0:8Ga0:2N heterostructure. In these experiments, we observe around zero time delay distinct phonon sidebands, whic disappear because of spectral diffusion with a time constant of 80 fs. The signal itself decays with a time constant of 380 fs. Th independent boson model agrees very...

We investigate midinfrared intersubband photodetectors based on short-period AlN/GaN superlattices with different quantum well thicknesses. Band structure calculations, as well as optical transmission and photovoltage measurements, underline the importance of higher order interminiband transitions. In particular, it was found that optical transitions between the second and third minibands benef...

Interwell optical-phonon-assisted transitions are studied in an asymmetric double-quantum-well heterostructure comprising one narrow and one wide coupled quantum wells (QW’s). We show that the depopulation rate of the lower subband states in the narrow QW can be significantly enhanced, thus facilitating the intersubband inverse population, if the depopulated subband is aligned with the second s...

Quantum cascade ~QC! lasers, based on intersubband transitions in semiconductor quantum wells, are characterized by ultrafast ~picosecond! carrier lifetimes. An important consequence of this unique property is the expected absence of relaxation oscillations in the transient response of these devices. Here, we discuss and experimentally verify this prediction by measuring the modulation response...

The coupling of spin waves with chargeand spin-density waves is shown to be induced by a spin-dependent interaction in a quantum well, which is spin polarized by a dc magnetic field at an angle u to the symmetry axis. The mixing of the plasmonic and magnonic modes, which occurs for both intraand intersubband transitions, depends on the coupling constant of the spin-spin interaction, the tilt an...

A key parameter underlying the efficacy of any nonlinear optical process is group velocity dispersion. In quantum cascade lasers (QCLs), there have been several recent demonstrations of devices exploiting nonlinearities in both the mid-infrared and the terahertz. Though the gain of QCLs has been well studied, the dispersion has been much less investigated, and several questions remain about its...

We demonstrate the capabilities of SILVACO TCAD tools for the design and simulation of intersubband GaAs/AlGaAs multiple quantum well infrared photodetectors. We compute the photoconductive gain spectrum of the device self consistently with the charge flow, non-radiative capture-escape, and intersubband transitions in the active region. The solid state calculations provide input to a light prop...