Modification of carrier localisation in basal-plane stacking faults: the effect of Si-doping in a-plane GaN
Badcock, T J and Kappers, M J and Moram, M A and Dawson, P and Humphreys, C J
The optical properties of Si-doped a-plane GaN epilayers grown on r-plane sapphire are studied. The low temperature emission is dominated by basal-plane stacking fault (BSF) recombination throughout the investigated doping range (1 × 1017 to 5 × 1019 cm−3). From temperature dependent photoluminescence (PL) measurements in conjunction with PL excitation studies, the carrier localization energy within the BSF is inferred to decrease from 17 meV to a negligible level as the doping density increases from 1 × 1017 to 5 × 1018 cm−3. It is proposed that electrons, ionized from the Si-donor atoms at the growth temperature, are able to transfer to the BSFs, where they progressively fill the available density of localized states. For doping levels in excess of 1 × 108 cm−3, the luminescence linewidth broadens significantly and the luminescence transients decay with a single exponential time constant. This behaviour is attributed to the onset of band-filling which causes a marked increase in the free electron density within the BSFs.
Department of Materials
Imperial College London
Royal School of Mines
London, SW7 2AZ - UK