Abstract
In this letter, we report on the impact aluminum has on gallium desorption kinetics in AlGaN alloys grown by gas source-molecular beam epitaxy. Aluminum is found to preferentially incorporate into the AlGaN films over the range of fluxes and temperatures investigated [0.05⩽Ji(Ga)⩽0.5 ML/s; 0.1⩽Ji(Al)⩽0.2 ML/s; 700 °C⩽Ts⩽775 °C]. As a result, Ga is not observed to incorporate into the film until the NH3 flux exceeds that required to grow stoichiometric AlN. This preferential incorporation stems from two facts: (a) Al has an ammonia cracking efficiency ∼2.5 times greater than that of Ga, and (b) Al participates in a Al-for-Ga exchange. As a result of these factors and under NH3 limited growth conditions, the aluminum mole fraction in a layer can be controlled by changing the incident NH3 flux.
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