Optical Properties and Defect Formation in Gallium Phosphide/Gallium Nitrogen Phosphide Core/Shell Nanowires

III-V semiconductor nanowires (NWs) have recently attracted increasing attention due to their potential applications in optoelectronic and photonic devices. Among all III-V compounds, GaP-based materials have the smallest lattice mismatch to Si are, therefore, among the best candidates for growth of III-V core/shell NWs on silicon. Adding a small amount of N in GaP allows one to further minimize this mismatch and also leads to transformation of the band gap character from an indirect one in GaP to a direct-like one in the GaNP alloys, leading to improvements in efficiency of light emission.

In this work we evaluate radiative efficiency of novel GaP/GaNP core/shell NWs grown on Si substrates by using comprehensive optical characterization techniques, including cw- and time-resolved photoluminescence (PL) spectroscopies and optically detected magnetic resonance (ODMR). Superior optical quality of the structures is demonstrated from the observation of intense PL emission from a single NW at room temperature (RT). This emission is concluded to originate from radiative transitions within N-related localized states, based on the results from the temperature dependent cw- and time-resolved PL studies. In spite of the high optical quality, the RT carrier lifetime in the structures is still found to be governed by non-radiative recombination processes as evident from the results of the time-resolved PL measurements. ODMR studies identified a defect complex involving a P atom at its core as a non-radiative recombination center in the GaNP shell, most likely located at the GaP/GaNP interface.