Chapter 13 - Theoretical aspects of strained-layer quantum-well lasers

Abstract

This chapter presents a theoretical model with the nonparabolic valence-band mixing and the many-body effects for strained-layer quantum-well lasers. The theoretical approach for the electronic properties is based on the Luttinger-Kohn Hamiltonian, taking into account the strains, or so-called the Pikus-Bir Hamiltonian. The effects of the biaxial compressive and tensile strains on the gain, the output characteristics, the band-gap renormalization, and the modulation response of strained-layer quantum-well lasers were studied. The effects of the spin-orbit (SO) split-off band coupling on the valence-band structure, density of states (DOS), dipole moment, and the linear and nonlinear optical gains of the strainedlayer quantum wells and compared them with the results obtained without accounting for the SO coupling have been calculated. The gain spectra calculated with the Lorentzian line-shape function show two anomalous phenomena: an unnatural absorption region below the band-gap energy and a mismatch of the transparency point in the gain spectra with the Fermi-level separation, the latter suggesting that the carriers and the photons are not in thermal (or quasi) equilibrium. The optical gain and the line-shape function of the quantum well under an external optical field were derived fromrecently developed time-convolutionless quantum-kinetic equations for electron-hole pairs near the band edge. Many-body effects, such as band-gap renormalization and excitonic enhancement, are included by taking into account the Coulomb interaction in the Hartree-Fock approximation. It is shown that the non-Markovian gain model with many-body effects removes the two anomalies associated with the Lorentzian line-shape function.