Photomodulated reflectivity studies of semiconductors under pressure

Photomodulated Reflectivity, Photoluminescence, and Raman Scattering studies of strained single epilayer, quantum well, and ordered alloy heterojunctions under pressure are presented. The pressures range from 1-bar to 70-kbar and temperatures 8-K to 300-K. All samples are grown by Molecular Beam Epitaxy or Organometallic Chemical Vapor Deposition. Various band edge or confined transition energies are measured as a function of pressure to determine pressure coefficients and/or pressure dependent strain effects. The heterojunctions studied are the ZnSe/GaAs, CdTe/InSb, and ZnTe/InAs epilayers, a Zn{dollar}sb{lcub}0.82{rcub}{dollar}Cd{dollar}sb{lcub}0.18{rcub}{dollar}Se/ZnSe set of quantum wells, and an epilayer of an ordered alloy of InGaP{dollar}sb2{dollar}.; In addition to inherent biaxial strains in semiconductor heterostructures due to lattice mismatch, external hydrostatic pressures can induce biaxial strains due to differences in the compressibilities of respective layers. This allows the tuning of interlayer strains as a function of pressure. In addition one has the opportunity to study not only biaxially strain effects, but the effects of combining interlayer strains with quantum confinement and spontaneous ordering in these materials.; The measurements which appear in this work address the following issues: (1) The shear deformation potential which describes properties of the band structure under a biaxial stress has been measured for ZnTe as a function of applied pressure (or volume). It has been found to be pressure (strain) dependent, supporting earlier results in ZnSe. (2) The temperature dependence of strain is measured in ZnSe on GaAs in order to compare several experiments on this system performed at differing temperatures. (3) The strained CdTe on InSb system is studied as a function of pressure(strain) and an increased magnitude of interlayer strain is measured as pressure is increased. The epilayer is found to support a strain larger than predicted by simple theories. (4) The lowest confined levels in strained Zn{dollar}sb{lcub}0.82{rcub}{dollar}Cd{dollar}sb{lcub}0.18{rcub}{dollar}Se quantum wells are measured as a function of pressure and the results are compared to calculations. (5) Energy levels near the direct gap of InGaP{dollar}sb2{dollar} ordered alloy, grown on GaAs, are examined and compared to theories predicting the combined effects of strain and ordering.; These experiments illustrate the power of optical spectroscopies and hydrostatic pressure combined to study strain, quantum confinement and ordering effects.