Metalorganic vapour phase epitaxial growth on vicinal GaAs (001) surfaces studied by reflectance anisotropy spectroscopy

Abstract

Structure and growth dynamics of vicinal GaAs (001) surfaces during metalorganic vapour phase epitaxy (MOVPE) are studied using reflectance anisotropy/difference spectroscopy (RAS or RDS). Spectra at different temperatures from (001)-surfaces tilted with angles between 0° and 6° towards the [110]- or [110]-axis are compared to those taken from nominally untilted (singular) surfaces. Under AsH3 stabilized conditions singular surfaces show c(4×4)-like RAS spectra for temperatures up to around 900 K. This type of spectrum is only observed at lower temperatures for vicinal surfaces. At higher temperatures RAS spectra which are characteristic of Ga dimer formation are obtained. The temperature at which this change from an As dimer- to a Ga dimer-dominated spectrum occurs, decreases with increasing misorientation angle and thus increasing number of steps. These results strongly indicate that there is an arsenic deficiency at steps resulting in formation of Ga dimers. Similarly, spectra during growth of vicinal surfaces show enhanced coverage with Ga dimers compared to those of singular surfaces. Growth kinetics, however, does not seem to be influenced by the presence of steps. The growth dynamics are studied in dependence of the misorientation by time-resolved RAS measurements. RAS monolayer oscillations are observed only for misorientations up to 2°. The temperature, above which the oscillations disappear, decreases with increasing misorientation. This confirms that the upper temperature limit for the existence of MOVPE-RAS growth oscillations is given by the transition from island- to step flow-growth mode. In contrast to typical molecular beam epitaxy (MBE) growth large diffusion lengths need to be assumed in MOVPE but the differences between different misorientation directions turn out to be small.