Modification of GaAs(100) and GaN(0001) surfaces by treatment in alcoholic sulfide solutions

The properties of the surfaces of GaAs(1 0 0) and GaN(0 0 0 1) passivated in aqueous and alcoholic sulfide solutions have been studied by using photoluminescence, X-ray photoelectron spectroscopy and atomic force microscopy. We have suggested the conception, which describes the effect of solution on the electronic properties of sulfidizing semiconductor surface. According to this conception, the density of surface states pinning the Fermi level should decrease with the increase of global hardness of electron cloud of atom or ion after sulfide passivation. It has been shown that the hardness of the sulfur ion increases with the decrease of charge of ion and with the decrease of dielectric constant of the solvent. It has been found that treatment of GaAs(1 0 0) and GaN (0 0 0 1) in alcoholic sulfide solutions results in the effective surface passivation. With the decrease of the solution dielectric constant the surface sulfur coverage increases, the thickness of the native oxide layer decreases and the efficiency of band-edge photoluminescence increases. These dependencies are stronger for solutions of strong base salt (e.g., sodium sulfide) than for that of weak base salt (e.g., ammonium sulfide). The chemical-kinetic effect has been observed: the greatest effect on the electronic properties of the semiconductor is achieved when the solution with the highest sulfur chemical activity is used. It was shown that the small-scale surface relief of the layer of GaN is largely smoothed with the sulfide treatment. The sulfide passivation in alcoholic solutions was applied for facet passivation of InGaAs/AlGaAs lasers (lambda = 977 nm) and GaAs power diodes. (C) 2002 Elsevier Science Ltd. All rights reserved.