We demonstrated an observation of excited gallium (Ga) emission by op
tical emission spectroscopy (OES) during GaN growth. It was also demon
strated that crystal structure of GaN could be controlled by changing
bias conditions during electron-cyclotron-resonance plasma-excited mol
ecular beam epitaxy (ECR-MBE). Change of GaN crystal structure from he
xagonal to cubic (c-) by applied positive bias voltage to the substrat
e was observed for the first time. Growth of c-GaN and decrease in Ga
emission intensity in deeper positive bias conditions were successful
ly explained by suppression of Ga desorption. From these observations,
OES is demonstrated to be useful as the monitoring tool in ECR plasma
-excited MBE. (C) 1998 Elsevier Science B.V. All rights reserved.