AVS 46th International Symposium
    Electronic Materials and Processing Division Monday Sessions
       Session EM-MoM

Paper EM-MoM7
Growth Kinetics of GaN(0001) as Grown by MBE@footnote1@

Monday, October 25, 1999, 10:20 am, Room 608

Session: Nitride Epitaxy
Presenter: A. Parkhomovsky, University of Minnesota
Authors: A. Parkhomovsky, University of Minnesota
S.M. Seutter, University of Minnesota
B.E. Ishaug, University of Minnesota
A.M. Dabiran, University of Minnesota
P.I. Cohen, University of Minnesota
S. Keller, University of California, Santa Barbara
S.P. DenBaars, University of California, Santa Barbara
Correspondent: Click to Email
The kinetics of growth of GaN films using molecular beam epitaxy with a Ga K-cell and an NH@sub 3@ leak was studied. GaN(0001) layers grown by metalorganic chemical vapor deposition on c-plane sapphire were used as substrates. In situ growth monitoring was conducted using reflection high energy electron diffraction (RHEED) and desorption mass spectroscopy (DMS). The films were characterized in situ by UHV scanning tunneling microscopy (STM) and ex situ by atomic force microscopy. Prior to the growth the substrates exhibited a 2D RHEED pattern characteristic of a smooth surface with atomic steps. Initial growth of GaN under Ga rich conditions on this surface at 760°C produced a rough surface as indicated by a 3D RHEED pattern. We suggest that the roughening is due to a surface contamination that changes the growth kinetics, causing faceting of the surface. The surface was then gradually smoothened by growing under the same excess Ga conditions. On a smooth surface, RHEED intensity oscillations were observed for both the excess Ga and excess NH@sub 3@ growth regimes. This is very different from the GaN(000-1). Like the GaN(000-1), the RHEED oscillations were observed in the excess NH@sub 3@ regime at Ga beam equivalent pressures ranging from 3x10@super-7@ to 5x10@super-7@ Torr and an ammonia BEP from 0.5x10@super-4@ Torr to 1.0x10@super-4@ Torr at a substrate temperature of 600°C. Unlike GaN(000-1), the RHEED oscillations were seen in the excess Ga regime at a Ga BEP of 1.4x10@super-6@ Torr, NH@sub 3@ BEP of 1.6x10@super-7@ Torr and at a substrate temperature of 760°C. Upon initiation of the Ga flux, DMS measurements indicated a single step increase in the Ga desorption signal which is different from the two-step increase on the GaN(000-1) associated with a physisorbed state. UHV STM studies were conducted on fully gallided and partially nitrided quenched GaN surfaces. Partial nitridation of GaN(0001) surface in ammonia produced nitrided zones at step edges that are 15-20 nm in size and 2-3 ML deep. The size of the zones is much less than that on the GaN(000-1) surface. @FootnoteText@ @footnote1@ Partially supported by the Office of Naval Reasearch and the National Science Foundation