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 (1×10 17 to 5×10 19cm -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 17meV to a negligible level as the doping density increases from 1×10 17 to 5×10 18cm -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 1×10 18cm -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.
- a-plane GaN
- Basal-plane stacking fault