Spectroscopic Study of Alloy Semiconductors GALLIUM(1 - Aluminum(x) Gallium-Arsenide and (GALLIUM(1 -X)ALUMINUM(X))0.47 Indium 0.53 Indium-Phosphide

The semiconductor alloy systems Ga(,1-x)Al(,x)As/GaAs (0 < x < 0.9) and (Ga(,1-x)Al(,x))(,0.47)In(,0.53)As/InP (0 <= x <= 1) and their interfaces with the substrates are investigated using three spectroscopic techniques, i.e., Raman scattering (RS), electroreflectance (ER) and nuclear profiling. Using a "spatial correlation" model with a Gaussian correlation function we have for the first time quantitatively explained the broadening and asymmetry of the first-order longitudinal-optic phonon Raman spectrum induced by alloy potential fluctuations. The systems studied were the representative alloy systems Ga(,1-x)Al(,x)As/GaAs and Ga(,0.47)In(,0.53)As/InP. This analysis provides important insights into the microscopic nature of the alloy potential fluctuations. We have performed the first ER study on the quaternary alloy system (Ga(,1-x)Al(,x))(,0.47)In(,0.53)As grown lattice matched to InP. The various interband transition energies E(,0) (fundamental gap), E(,0)+(DELTA)(,0) (spin orbit split component), E(,1), E(,1)+ (DELTA)(,1), E(,0)' + (DELTA)(,0)' as well as the spin orbit splittings of the valence bands (DELTA)(,0) and (DELTA)(,1) were accurately determined. The spin orbit splittings (DELTA)(,0) and (DELTA)(,1) exhibit a negative bowing similar to that found in the other quaternary alloy system GaInAsP. We have generalized the VV-B-W model including both intra and interband effects to account for the composition dependence of the valence band spin orbit splittings (DELTA)(,0) and (DELTA)(,1) in the quaternary alloys InGaAsP and GaAlInAs grown lattice matched to InP. The effects of substrate preparation on the properties of the epitaxial layer are investigated in GaAlAs/GaAs heterojunctions prepared by different modifications of liquid phase epitaxy using RS as well as ER. Signals were observed from both the GaAlAs epilayer and the GaAs substrate at the interface. The results are correlated with the properties of the substrate and growth condition. The major limitation to the depth resolution in depth profiling using ion beams is the energy straggling of the projectiles resulting from the statistical nature of the energy loss mechanism. We have done the first energy straggling measurements in GaAlAs using nuclear reaction technique. The samples were prepared by MBE. We have also observed the importance of growing buffer layers to obtain sharp interfaces in GaAlAs/GaAs heterostructures.