Devin Crawford, R. Held, A. M. Johnston, A. M. Dabiran, and P. I. Cohen, Department of Electrical Engineering, University of Minnesota, 200 Union St. SE Minneapolis, MN 55455 USA
The First European GaN Workshop, EGW-1, June 2nd - 4th, 1996, Rigi, Switzerland.
Abstract
MBE growth of GaN on c-plane sapphire has been studied using in-situ RHEED and reflection mass-spectroscopy. Changes in reflected species are correlated with RHEED intensity variations. An increase in the reflected H2 signal combined with a decrease in the reflected N2-H complexes upon commencement of growth suggest that GaN growth proceeds via formation of intermediate nitrogen-hydrogen adsorbates. A single RHEED intensity oscillation upon opening the Ga shutter is consistently observed on smooth samples under highly Ga rich growth conditions. The period of the oscillation increases with increasing ammonia flux, suggesting that the oscillation is chemical rather than structural in nature. We attribute this change in intensity to an increase in the electron scattering factor resulting from a change in surface chemistry and reconstruction. During growth (Ga rich) the RHEED indicates a 1X1 reconstruction, while a weak 2X2 reconstruction can be observed when growth has been terminated.
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