ELECTRICAL AND OPTICAL-PROPERTIES OF OXYGEN DOPED GAN GROWN BY MOCVD USING N2O

Oxygen doped GaN has been grown by metalorganic chemical vapor deposit ion using N2O as oxygen dopant source. The layers were deposited on 2' ' sapphire substrates from trimethylgallium and especially dried ammon ia using nitrogen (N-2) as carrier gas. Prior to the growth of the fil ms, an AIN nucleation layer with a thickness of about 300 Angstrom was grown using trimethylaluminum. The films were deposited at 1085 degre es C at a growth rate of 1.0 mu m/h and showed a specular, mirrorlike surface. Not intentionally doped layers have high resistivity(> 20 kW/ square). The gas phase concentration of the N2O was varied between 25 and 400 ppm with respect to the total gas volume. The doped layers wer e n-type with carrier concentrations in the range of 4 x 10(16) cm(-3) to 4 x 10(18) cm(-3) as measured by Hall effect. The observed carrier concentration increased with increasing N2O concentration. Low temper ature photoluminescence experiments performed on the doped layers reve aled besides free A and B exciton emission an exciton bound to a shall ow donor. With increasing N2O concentration in the gas phase, the inte nsity of the donor bound exciton increased relative to that of the fre e excitons. These observations indicate that oxygen behaves as a shall ow donor in GaN. This interpretation is supported by covalent radius a nd electronegativity arguments.