We study effects of modulation doping in a type-II quantum well by performing a self-consistent band structure calculation using the 8-band k • p theory. We show that modulation doping can convert a type-II quantum well structures into type-I. The associated band bending and charge redistribution lead to strong interband transition in such type-II structures comparable to that of a type-I quantum well. The results are shown for InAs/AlSb quantum well, where TM mode optical gain can be as high as 4000cm-1. We also studied effects
of doping on differential gain.
Intersubband absorption spectra are analyzed using the density matrix theory under the second Born approximation. The intersubband semiconductor Bloch equations are derived from the first principles including electron-electron and electron-longitudinal optical phonon interactions, whereas electron-interface roughness scattering is considered using Ando's theory. A spurious-states-free 8-band
k•p Hamiltonian is used, in conjunction with the envelope function approximation to calculate the electronic band structure self-consistently for type II InAs/AlSb multiple quantum well structures. We demonstrate the interplay of various physical processes in the absorption spectra in the mid-infrared frequency range.
We developed a method to eliminate the spurious solutions of the
k•p Hamiltonian in the envelope function approximation applied to the quantized states of heterostructures by introducing an off-diagonal k2 term. This results in a modification in the fourth and higher order terms in k of the band dispersion, which keeps the dispersion at the Γ point but modifies it at large k so that converts spurious states to the harmless evanescent ones. We show that the modification to the Hamiltonian leads to the monotonic behavior of the conduction band as a function of k and thus removes the spurious solutions in the calculations of confined states for all popular III-V compounds and their alloys.
The influence of light illumination and high electric field pulses on the long-term relaxation effect in piezoresistivity which has been discovered recently in p- GaAs/Al0.5Ga0.5As heterostructures has ben investigated. Significant acceleration of relaxation processes has been observed under the carriers heating by different external sources. This means that these phenomena are mostly determined by nonequilibrium processes in electron system. At 4.2 K under high electric fields switching of the samples to long-term high-resistance state has ben also found.
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