Intersubband absorption in Si 1-xGe x/Si and δ-dope Si multiple quantum wells

Abstract

The hole intersubband infrared absorption in SiGe/Si and δ-doped Si multiple quantum wells is reported. Typical structures consist of 10 periods of 300 Å thick undoped Si barriers and either SiGe quantum wells of 48 Å or boron doped Si quantum wells of 35 Å wide. Near 100% infrared absorption is measured by a FTIR spectrometer using waveguide structures. The polarization dependent spectra show good agreement with the intersubband selection rule. In SiGe/Si multiple quantum well structures, the transition energy depends on the Ge fraction and the well thickness and 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 turned by varying the doping concentration in the δ-doped layer. The experimentally observed transition energy positions are considerably higher than that estimated using the Hartree approximation. With the inclusion of the many-body effect, the hole-hole exchange interaction, the estimated subband energy separations are in close agreement with the experimentally observed values. This observation suggests that the multiple quantum well IR detectors may be used for Si-based optoelectronics.