Cavity-Enhanced Microphotoluminescence in a Core–Shell n–p CdS/CdO Micrometer Wire and Its Efficient Surface Photovoltage Responses in the Whole Visible Range

Abstract

A one-step growth of yellow and red CdS:O wires has been realized by a SnO2-catalyzed chemical vapor deposition (CVD) technique. The yellow and red CdS:O wires were obtained upon the temperature rising rates in the tube furnace. Yellow nanowire with less oxygen doping shows luminescent behavior from the acceptor trapped excitons near the band edge of the CdS nanowire. The X-ray diffraction (XRD) and transmission electron microscopy (TEM) characterizations proved their formation of the CdS/CdO core–shell red wire due to O segregations in the CdS lattice when the oxygen doping concentration was higher than 4%, even up to 20%. Their microluminescence profiles are mainly caused by the CdO shell in the red wire, which gives temporally localized exciton emissions near the CdO band edge (600 nm) by femtosecond-pulse excitation and red-shift enhanced whispering-gallery mode (WGM) cavity mode emissions by a 488 nm continuous wave (CW) laser excitation. The luminescence of the CdS/CdO wire reflects the electronic state modification for CdO nanowires with no luminescence due to the p–n junction formation. The photovoltaic (PV) spectra of yellow and red wire aggregates show CdS and CdS/CdO profiles, respectively. The CdS/CdO wires have an extended PV responses from 510 to 800 nm as compared with CdS, the photocarrier type in the 300–510 nm range likes n-CdS, while that in the 510–800 nm range is p-type from the CdO shell. Both luminescence and PV responses could be enhanced by the WGM mode and core–shell n–p junction within a wire with dual PV zones. Such wires can find potential applications in the solar cells and nanophotonic devices.