On mechanisms governing AlN and AlGaN growth rate and composition in large substrate size planetary MOVPE reactors.

Abstract: We report about a MOVPE parameter study carried out on a Planetary Reactor to determine factors that govern the incorporation efficiency of aluminum and gallium into Al x Ga1−x N, hence its solid composition x and growth rate. Parameter variations include pressure, flow rate, wafer and ceiling temperature, V–III-ratio, and Al/(Al+Ga) inlet ratio. The target composition is 0.15<x<0.4. Losses of nutrients due to gas phase reactions between metalorganics and ammonia were suppressed by choosing operational conditions of low pressure and relatively low V–III ratios. The temperature dependence of composition x is instead accounted for by selective desorption of gallium from the layer surface which occurs independent of epitaxial growth and which aluminum is not subject to. The diminution of partial GaN growth rate in Al x Ga1−x N due to this phenomenon is found to depend not only on temperature but also on ammonia partial pressure and the solid composition of Al x Ga1−x N. The rate of growth rate reduction by this effect is determined quantitatively by comparing experimental growth data with modeling prediction of gallium incorporation computed by disregarding the desorption kinetics. Based on the obtained data the gallium desorption rate was found to follow an Arrhenius temperature dependence with an activation energy of E a =2.1eV. [Copyright &y& Elsevier]