The surface preparation of GaSb(100), based on HCl solutions, was studied by x-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The chemical and structural analysis by XPS and AFM indicates that the GaSb surface treated by HCl followed by a 2-propanol rinse leads to a 1 to 2 nm oxide layer on the surface. The resulting smooth surface is slightly antimony rich. Surfaces rinsed in deionized water, after HCl-based etching, possess a thicker overlayer, which is depleted of antimony. The surface morphology becomes rough rapidly upon reexposure to air after the HCl/H2O treatment. Other etching processes, including a tartaric acid based etchant, were investigated. Tartaric acid-based etches yield a highly nonstoichiometric surface along with an inhomogeneous etching morphology. The rates of desorption of surface oxides were determined by XPS analysis under ultrahigh vacuum conditions and the typical temperatures of desorption for the constituent chemical component comprising the surface layer were determined.

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Pseudomorphic four-period GaAs 0.978 N 0.022 / GaAs 0.78 Sb 0.22 type-II multiquantum well structures were grown on ͑100͒ GaAs substrates by metalorganic vapor phase epitaxy at 530°C. The GaAs 0.978 N 0.022 layers were grown at a V/III ratio of 685 and N / V ratio of 0.96, whereas the GaAs 0.78 Sb 0.22 was grown at a V/III ratio of 3.8 and Sb/ V ratio of 0.8. The superlattice peaks in the x-ray diffraction -2 scans around the ͑400͒ GaAs peak were fitted using a dynamical simulation model to determine layer thickness and alloy compositions. The GaAsN and GaAsSb thicknesses were ϳ8 nm and ϳ5 nm, respectively. The photoluminescence ͑PL͒ spectra were obtained at 30 K and the PL peak energy was found to match the type-II transition energy obtained from a 10-band k · p model. Postgrowth annealing under arsine-H 2 with a N 2 cooldown was found to increase the low temperature PL intensity and result in the appearance of luminescence at room temperature.

Near-field scanning optical microscopy (NSOM) was used to study cleaved edges of GaAs solar cell devices. Using visible light for excitation, the NSOM acquired spatially resolved traces of the photocurrent response across the various layers in the device. For excitation energies well above the band gap, carrier recombination at the cleaved surface had a strong influence on the photocurrent signal. Decreasing the excitation energy, which increased the optical penetration depth, allowed the effects of surface recombination to be separated from collection by the pn junction. Using this approach, the NSOM measurements directly observed the effects of a buried minority carrier reflector/passivation layer.