Zn and S Doping in GaAs Selective Area Growth by Metal–Organic Vapor Phase Epitaxy

Abstract

The surface reaction rate constant (ks) is one of the most important parameters in metal–organic vapor phase epitaxy (MOVPE), since it affects the growth rate and the composition of the epitaxial layer in selective area growth (SAG). It is possible to predict the properties of the epitaxial layer from the value of ks. The value of ks can be extracted through a two-dimensional numerical simulation of SAG, and it strongly depends on growth conditions. In this paper, zinc and sulfur doping in GaAs SAG are studied. It is shown that the ks of GaAs is independent of dopant input pressure at low Zn or S pressure. This implies that under these conditions, the growth rate will not be affected by doping. Furthermore, the database of ks values based on undoped GaAs-SAG can be used directly in doping processes. The ks value is reduced when Zn input pressure is of the same order of magnitude as Ga partial pressure. When the mask width is less than 100 µm, the masks will not influence ks. However, the ks value is reduced when 200 µm masks are used due to the excessive enhancement of trimethylgallium local pressure, which leads to a nonlinear reaction mode. The dopant concentration in SAG samples has been measured using secondary ion mass spectroscopy (SIMS). The effect of mask width on dopant incorporation can be simplified as the effect from Ga-species pressure. Zn concentration in the epitaxial layer is nearly independent of Ga partial pressure or the mask width. S concentration increases with increasing Ga partial pressure. These phenomena can be understood from their doping behavior and reactions. With increasing mask width, S incorporation in GaAs slightly increases, but is reduced when 200 µm masks are used. This reduction may be caused by the adsorption of S species on SiO2 masks.