Photoluminescence setup

The optical measurements have been performed in a closed-cycle He cryostat. A continuous wave laser at 532 nm was used for above bandgap excitation for all photoluminescence measurements, while a 400 nm pulsed laser (temporal pulse full width half maximum ~90 ps) was used for lifetime measurements. Scanning-PL measurements have been performed in a micro-PL configuration, scanning in a straight line for 30 s on the sample kept at 2 K (except for temperature dependent PL measurements). The spectrum is measured using a low-noise charge-coupled device connected to a 75 cm long spectrometer. The same setup, has been used for micro-PL measurements of individual nanowires. Macro-PL measurements have been done using a similar setup, with a lens with larger focal length, without any scanning. The lifetime is measured with a fast single-photon detector (~50 ps jitter) combined with time-tagging electronics (~100 ps jitter).