Phosphorous doping in vertically aligned ZnO nanorods grown by wet-chemical method

Abstract

The synthesis of well-aligned highly crystalline phosphorous (P) doped ZnO nanorods (ZnO:P) on glass substrates is demonstrated here. Vertically aligned ZnO nanorods are fabricated by a two-step method comprises of nanocrystalline ZnO seed layer formation by dc sputtering technique followed by solution growth of ZnO nanorods. To incorporate P, aligned ZnO nanorod films are exposed to P vapor in a vacuum chamber and then subjected to rapid thermal annealing in vacuum at an elevated temperature of 450 °C. Scanning electron microscopy and X-ray diffraction measurement confirm the growth of highly crystalline well aligned hexagonal ZnO nanorods that are perpendicular to the substrate surface. The optical band gap estimated from the transmittance spectra recorded by a UV–VIS–NIR spectrophotometer is 0.24 eV lower for ZnO:P compared to ZnO nanorods. Vibrational properties of ZnO:P nanorods are studied by FTIR and Raman spectra. Raman peak appeared at 355 cm−1 for ZnO:P is due to the Zn-site substituted by phosphorous. For ZnO nanorods, the room temperature photoluminescence (PL) spectra shows a sharp UV emission peak due to near band edge transition and a broad blue–green emission peak due to defect related transition. The observed red shift for the UV emission peak in the ZnO:P nanorods is associated with the shrinking band gap whereas the intense and broad blue–green emission peak is due to defects introduced with P doping.