Optical Response of Ultrathin GaP Nanoantenna with Zincblende-to-Wurtzite Crystal Phase Transitions

The crystal structure of III–V semiconductor nanowires (NWs) depends on growth conditions such as the atomic V/III flux ratio and the growth temperature, facilitating crystal phase engineering. For example, GaP NWs may adopt the indirect bandgap zincblende (ZB) phase or direct bandgap wurtzite (WZ) phase depending on growth conditions. In this work, we study the optical response of GaP NWs grown by molecular beam epitaxy that exhibit crystal phase transitions between ZB and WZ. Spatially resolved cathodoluminescence and Raman measurements show spectral changes that coincide with the crystal structure mapped by electron microscopy. In particular, WZ GaP luminescence is characterized by a bound exciton with energy 2.141 eV at 10 K while twinned ZB GaP yields peaks in the energy range 2.15–2.28 eV, which have not been previously reported in literature. We attribute the unknown peaks to coupled QWs formed by closely spaced twin boundaries and calculate relevant transition energies using a one-dimensional Schrödinger-Poisson solver. Recombination facilitated by two defect levels in twinned ZB GaP is also noted. These results demonstrate the characterization of NW crystal structure and defects by optical spectroscopic methods.