The effect of Al on Ga desorption during gas source-molecular beam epitaxial growth of AlGaN

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 less than or equal to J(i)(Ga) less than or equal to 0.5 ML/s; 0.1 less than or equal to J(i)(Al) less than or equal to 0.2 ML/s; 700 degrees C less than or equal to Ts less than or equal to 775 degrees C]. As a result, Ga is not observed to incorporate into the film until the NH3 flux exceeds that required to grow stoichiometric AIN. This preferential incorporation stems from two facts: (a) Al has an ammonia cracking efficiency similar to 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. (C) 1998 American Institute of Physics.