| Photoreflectance and Photoluminescence studies of several strained-layer semiconductor heterojunctions under pressure are presented. The pressures range from 1Bar to 70kBars and the temperature from 6K to 300K for the various studies. All samples were high quality Molecular Beam Epitaxially grown samples. Various band edge or confined transition energies are measured as a function of pressure and accurate pressure coefficients are determined. The heterojunctions studied are the ZnSe/GaAs pseudomorphic epilayer, In{dollar}sb{lcub}0.21{rcub}{dollar}Ga{dollar}sb{lcub}0.79{rcub}{dollar}As/GaAs Single Quantum Well and two GaSb/AlSb Multiple Quantum Wells.; In addition to the built in biaxial strains in strained-layer systems due to lattice mismatch, external hydrostatic pressures can induce biaxial strains which may be tensile or compressive. These pressure dependent biaxial strains come from the fact that the heterojunction is grown on a comparatively thick substrate which may have a different compressibility. Under pressure the change in lattice constant perpendicular to the growth direction is governed by the thick substrate and additional pressure dependent biaxial strains are induced. The magnitude of these pressure induced strains can be very large. Our experiments show that the ZnSe/GaAs epilayer which is initially under biaxial compressive strain, becomes unstrained, and then tensile as a function of pressure. In contrast, in the GaSb/AlSb MQW grown on GaAs, the pressure induced strains augment the built in strains. A detailed study of these competing effects is presented. |
