SYNTHESIS AND RESONANCE RAMAN-SPECTROSCOPY OF CDS NANO-WIRE ARRAYS

Highly anisotropic arrays of aligned semiconductor nano-wires with dia meters in the range 9-22 nm and lengths up to 1 mu m were fabricated b y electrodepositing CdS into the pores of anodic aluminum oxide, The v alue of the exciton energy of the semiconductor nano-wires was determi ned as a function of wire diameter from the excitation wavelength depe ndence of their polarized resonance Raman spectra in the vicinity of t he CdS absorption edge, The resonance Raman (RR) spectra were dominate d by a progression in the longitudinal optical phonon mode, The relati ve intensities of the members of the progression are both excitation-w avelength and particle-size dependent. The LO phonon frequency was als o found to be wire-diameter dependent. The RR spectra were found to be almost independent of the polarization of the light exciting them. Th e optical exciton energy was determined to vary from 2.36 eV for the l argest diameter wires to 2.42 eV for the smallest. The absence of pola rization dependence is interpreted to be in part due to the fact that the nano-wires consist of strings of semiconductor crystallites so tha t the local aspect ratio of the crystallites is both not very great an d not uniform in the axial direction. For the smallest nano-wires the radial size uniformity is, however, very high. The dependence of the b and-gap energy on the diameter of the nano-wires is in good agreement with theory.