CHARACTERIZATION OF MID-GAP STATES IN HVPE AND MOVPE-GROWN N-TYPE GAN

Optical-isothermal capacitance transient spectroscopy (O-ICTS) is used to characterize the mid-gap states in n-type GaN grown by hydride vap or phase epitaxy and metalorganic vapor phase epitaxy. Deep levels are resolved by the emission rate of carries in addition to the magnitude of the capacitance transient as a function of incident photon energy. The mid-gap region is dominated by a distribution of traps from which carriers photoionize to the conduction band in the range of about 1.5 to 2.5 eV; these traps are suspected of participating in the frequent ly observed yellow luminescence. The concentration of these mid-gap st ates are found to be lowest in thick HVPE-grown GaN films. (C) 1998 El sevier Science B.V. All rights reserved.