Modification of carrier localization in basal-plane stacking faults: The effect of Si-doping in a-plane GaN

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.