Wurtzite gallium phosphide has a direct-band gap

Gallium Phosphide (GaP) with the normal cubic crystal structure has an indirect band gap, which severely limits the emission efficiency. We report the fabrication of GaP nanowires with pure hexagonal crystal structure and demonstrate the direct nature of the band gap. We observe strong photoluminescence at a wavelength of 594nm with short lifetime, typical for a direct band gap. Furthermore, by incorporation of aluminum or arsenic in the GaP nanowires, the emitted wavelength can be tuned across an important range of the visible light spectrum (555-690nm). This approach of crystal structure engineering enables new pathways for tailoring materials properties enhancing functionality.