Quantum Well Engineering for Intersubband Transitions-General Conduction Band Extrema and Valence Valley

Abstract

The physics and engineering of intersubband transitions are discussed. For the conduction intersubband transition, the effective mass tensor formulation is used to more generally illustrate the absorption behavior. For Si <110> quantum wells, for example, interconduction subband absorption is shown to be allowed for both s-and p-polarized optical fields, in contrast with the F valley of AlGaAs/GaAs case where only the s-polarization is possible. For intervalence bands, we have used SiGe/Si and δ-doped structures as examples. The hole intersubband infrared absorption in SiGe/Si and δ-doped Si multiple quantum wells is reported. The polarization dependent spectra show good agreement with the intersubband selection rule. In SiGe/Si multiple quantum well structures, the transition between the first two heavy hole subbands are observed. In the case of the δ-doped structures, the resonance absorption and peak energy can be tuned by varying the doping concentration in the δ-doped layer. The experimentally observed transition energy levels are in agreement with the calculated values when self consistency and the many-body effect, the hole-hole exchange interaction, are included. The possible selection rules are discussed.

In the engineering of intersubband transition, it is shown the transition between two bound states with spatially separated wave functions may have as much as a two-orders of magnitude increase in low field Stark shift, while maintaining a similar strong oscillator strength. Using an asymmetric quantum well, the selection rule, △n = odd is lifted.