Intra-valence-band mixing in strain-compensated SiGe quantum wells

TL;DR

This study investigates the midinfrared absorption and valence band mixing in strain-compensated SiGe quantum wells, revealing how strain and temperature influence intersubband transitions and state mixing, with theoretical modeling supporting the findings.

Contribution

It provides a detailed experimental and theoretical analysis of valence-band mixing and intersubband transitions in strain-compensated SiGe quantum wells, highlighting the effects of strain and temperature.

Findings

Observation of intersubband transition energies around 0.5 eV.

Detection of hh-lh and hh-so state mixing through oscillator strength transfer.

Temperature-induced broadening indicating non-parabolic dispersion of hh2 states.

Abstract

We explore the midinfrared absorption of strain-compensated p-Si0.2Ge0.8/Si quantum wells for various well thicknesses and temperatures. Owing to the large band offset due to the large bi-axial strain contrast between the wells and barriers, the intersubband transitions energies from the ground state to the excited heavy hole (hh), light hole (lh) and split-off hole (so) states are resolved to ~0.5 eV. When hh2 is within ~30 meV of lh1 or so1 a partial transfer of the hh1-hh2 oscillator strength to the hh1-lh1 or hh1-so1 transitions is observed, which is otherwise forbidden for light polarized perpendicular to the plane of the wells. This is a clear sign of mixing between the hh and lh or so-states. A large temperature induced broadening of hh2 peak is observed for narrow wells indicating a non-parabolic dispersion of the hh2 states due to the mixing with the lh/so continuum. We found that the 6-band k.p theory gives a quantitative account of the observations. A possible role of many-body effects in the temperatureinduced negative peak shift is discussed.