Electric-field-dependent photoconductivity in CdS nanowires and nanobelts: exciton ionization, Franz-Keldysh, and Stark effects.
We report on the electric-field-dependent photoconductivity (PC) near the band-edge region of individual CdS nanowires and nanobelts. The quasi-periodic oscillations above the band edge in nanowires and nanobelts have been attributed to a Franz-Keldesh effect. The exciton peaks in PC spectra of the nanowires and thinner nanobelts show pronounced red-shifting due to the Stark effect as the electric field increases, while the exciton ionization is mainly facilitated by strong electron-longitudinal optical (LO) phonon coupling. However, the band-edge transition of thick nanobelts blue-shifts due to the field-enhanced exciton ionization, suggesting partial exciton ionization as the electron-LO phonon coupling is suppressed in the thicker belts. Large Stark shifts, up to 48 meV in the nanowire and 12 meV in the thinner nanobelts, have been achieved with a moderate electric field on the order of kV/cm, indicating a strong size and dimensionality implication due to confinement and surface depletion.
Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371.
Dehui
D
Li
Jun
J
Zhang
Qing
Q
Zhang
Qihua
Q
Xiong
D019187:Cadmium Compounds / Q000737:chemistry* / Q000528:radiation effects*; D004553:Electric Conductivity; D004574:Electromagnetic Fields; D007477:Ions; D008027:Light; D008422:Materials Testing; D049329:Nanostructures / Q000737:chemistry* / Q000528:radiation effects*; D018036:Selenium Compounds / Q000737:chemistry* / Q000528:radiation effects*
D019187:Cadmium Compounds; D007477:Ions; D018036:Selenium Compounds; C058667:cadmium selenide