Closed-loop MBE growth of droplet-free GaN with very metal rich conditions using Metal Modulated Epitaxy with Mg and In

摘要

Improvements to the Metal Modulated Epitaxy (MME) tech-nique are achieved through computer controlled shutter tran-sitions based on feedback from RHEED transients (S. D. Burnham and W. A. Doolittle, J. Vac. Sci. Technol. B 24, 2100 (2006) [1]), thus creating a closed-loop control system for nitride MBE, the first of its kind. A high-sensitivity 22 bit camera is used to determine when RHEED transients have subsided, upon which a shutter transition is initiated allowing the efficient buildup and depletion of the metal bilayer, which improves surface morphology and growth rate compared to the standard MME technique. RMS surface roughness was reduced by 41% by using this "Smart Shuttering" improve-ment to MME. A substantially higher peak concentration of Mg, approaching 2% atomic concentration, was achieved us-ing the MME technique. As expected, a negligible amount of In was incorporated into the very Ga-rich films. Using the new closed loop control system developed for MBE, the sur-face morphology was improved for GaN films while highly repeatable holes concentrations as high as 4.7×10~(18) cm~(-3) with 1.07 cm~2/V-sec mobility was obtained. This approach offers great promise for improved reproducibility and improved material quality.