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Eberly College of Arts and Sciences




GaN was grown by molecular beam epitaxy in an effort to determine nucleation and growth conditions which lead to high quality, single-crystal films. Atomic force microscopy (AFM) was used to show that growth under Ga-rich conditions promotes the nucleation of films with large nucleation domains leading to a lower density of intrinsic defects related to domain boundaries. These conditions are also shown to promote a 2-D growth mode resulting in films with a high degree of nucleation domain coalescence and surface roughnesses below 2 nm. Addition of atomic hydrogen, using a thermally-cracked source, is shown to increase the growth rate of Ga-rich growths by a factor of two. The hydrogen appears to be altering the growth kinetics to increase the residence time of nitrogen atoms at the substrate surface. The addition of hydrogen seems to have no effect on the material characteristics as probed by Hall measurements and photoluminescence. In addition, the RF source used to generate active nitrogen species was characterized by means of mass spectroscopy and optical emission spectroscopy. Under normal operating conditions for GaN growth, the source was shown to convert about 5% of the total nitrogen input into neutral, nitrogen atoms and about 0.03% into nitrogen ions which may cause crystal damage during growth.

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Chemistry Commons