Electrical and optical properties of oxygen doped GaN grown by MOCVD using N2O

Abstract

Oxygen doped GaN has been grown by metalorganic chemical vapor deposition using N2O as oxygen dopant source. The layers were deposited on 2″ sapphire substrates from trimethylgallium and especially dried ammonia using nitrogen (N2) as carrier gas. Prior to the growth of the films, an AIN nucleation layer with a thickness of about 300A was grown using trimethylaluminum. The films were deposited at 1085°C at a growth rate of 1.0 µm/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 were n-type with carrier concentrations in the range of 4×1016 cm−3 to 4×1018 cm−3 as measured by Hall effect. The observed carrier concentration increased with increasing N2O concentration. Low temperature photoluminescence experiments performed on the doped layers revealed besides free A and B exciton emission an exciton bound to a shallow donor. With increasing N2O concentration in the gas phase, the intensity of the donor bound exciton increased relative to that of the free excitons. These observations indicate that oxygen behaves as a shallow donor in GaN. This interpretation is supported by covalent radius and electronegativity arguments.