Optical detection properties of silicon-germanium quantum well structures

A study has been carried out on Si/SiGe multi-quantum well structures to determine their applicability as normal incidence infrared detectors in the spectral range of 2-12 {dollar}mu{dollar}m. The research effort was primarily experimental, however, extensive calculations were performed to initially explain the experimental data and then used to design subsequent structures. Multiple quantum well structures grown on both Si{dollar}lbrack 001rbrack{dollar} and Si{dollar}lbrack 110rbrack{dollar} substrates via molecular beam epitaxy were studied by photoluminescence, absorption, and photoresponse measurements over a wide parameter space. Variables included quantum well depth and width, well doping, number of wells and growth temperature. Well widths were varied from 20A to 50A, Ge composition from 10% to 60%, boron doping from {dollar}1times10rmsp{lcub}18{rcub}cmsp{lcub}-3{rcub}{dollar} to {dollar}8times10rmsp{lcub}19{rcub}cmsp{lcub}-3{rcub}{dollar}, number of wells from 5 to 30 and growth temperature from 550{dollar}spcirc{dollar}C to 710{dollar}spcirc{dollar}C.; Calculations using {dollar}k{lcub}cdot{rcub}p{dollar} theory and the envelope function approximation were performed to determine the position of the bound states in the wells, the amount of band mixing and the transition strengths for bound-to-bound transitions for Si{dollar}rmlbrack 001rmrbrack/Sisb{lcub}1-x{rcub}Gesb{lcub}x{rcub},rm Silbrack 110rbrackrm/Sisb{lcub}1-x{rcub}Gesb{lcub}x{rcub}{dollar}, and GaAs/AlGaAs quantum well structures. The Si{dollar}lbrack 110rbrack{dollar} structures have more allowed energy bands which are significantly mixed. A comparison was made between Si{dollar}lbrack 001rbrack/rm Sisb{lcub}1-x{rcub}Gesb{lcub}x{rcub}, Silbrack 110rbrack/Sisb{lcub}1-x{rcub}Gesb{lcub}x{rcub}{dollar} and GaAs/AlGaAs quantum well structures designed to operate in the 8-12 {dollar}mu{dollar}m region, and all three showed comparable momentum matrix elements.