Population inversion in optically pumped asymmetric quantum well terahertz lasers
Intersubband carrier lifetimes and population ratios are calculated for three- and four-level optically pumped terahertz laser structures. Laser operation is based on intersubband transitions between the conduction band states of asymmetric GaAs-Ga1−xAlxAs quantum wells. It is shown that the carrier lifetimes in three-level systems fulfill the necessary conditions for stimulated emission only at temperatures below 200 K. The addition of a fourth level, however, enables fast depopulation of the lower laser level by resonant longitudinal optical phonon emission and thus offers potential for room temperature laser operation.
Excitons in diffused quantum wells.
The Schrodinger equation corresponding to the potential profile resulting from manganese diffusion in CdTe-Cd 1-x Mn z Te quantum wells has been solved using a numerical method. Calculation of the exciton binding energies has allowed predictions of the effect of diffusion on the resulting optical properties of such quantum-well structures. In addition to the magnetic-field-dependent potential Profiles that accompany the diffusion process, it is shown that the ratio of the Zeeman splitting of the light- and Heavy-hole excitonic transitions is strongly dependent on the extent of the manganese diffusion. Consequently, this ratio can be used as a measure of the diffusion coefficient
Application of a total-angular-momentum basis to quantum-dot band structure.
Multiband envelope theory is reformulated in terms of a basis of total envelope and zone-center Bloch angular momentum. The k⋅p operator is scalar with respect to the total-angular-momentum operator and hence is block diagonal in its eigenbasis. The projections of the Hamiltonian into the F=1/2 and the F=3/2 subspaces of total angular momentum are derived and quantum-dot band structure is calculated in GaAs(AlGaAs) and InAs(GaSb) systems as an example application of the formalism.