Optically active InP nanowires were grown on a quartz substrate covered with a layer (100 nm) of hydrogenated amorphous silicon (a-Si:H) by metalorganic chemical vapor deposition (MOCVD), demonstrating that single-crystal semiconductor nanowires can be formed on non-single-crystal surfaces. Scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, cathodoluminescence (CL), and photoluminescence (PL) were used to characterize the structural and optical properties of the nanowires. The nanowires on a-Si:H grew in random directions with high density. The XRD suggests that nanowires having either hexagonal-close-packed or face-centered cubic lattices co-exist. The Raman spectrum shows peaks associated with transverse optical (TO) and longitudinal optical (LO) branches of InP. The CL intensity does not vary signi?cantly along the growth direction and appears to be originated from the entire structure of the nanowire when probed at various positions. The CL data suggests that recombination is slow enough to allow the carriers to diffuse the complete length of the nanowires (˜2 m in length) before recombining. The PL spectrum suggested the nanowire had a part that contributes to the observed blue shift while the other part had nearly bulk feature in their structure.