Emission spectra of hexagonal zinc oxide microrods due to resonant modes

Abstract

Experimental observation and theoretical analysis of the whispering gallery mode (WGM) related emission spectra of ZnO microrods with a hexagonal cross-section are reported. ZnO microrods of various sizes are fabricated, and their individual geometric information (including the inner radius, edge profile modification, and tilt angle) are characterized via scanning electron microscopy (SEM). The photoluminescence spectra in the visible range (with energies between 1.77 and 2.76 eV) are compared with theoretical simulation based on Green function calculation within a nearly complete set of basis functions. WGM resonance peaks for TE and TM modes of five different sizes of microrods are analyzed. By using the SEM determined geometry with a slight adjustment, we obtain realistic simulation of the line shapes of the emission spectra, which agree well with experimental observation. To gain better understanding of the WGM resonance modes, we also calculate the WGM resonance profile of ZnO microrods with the cylindrical cross-section for both TE and TM modes for comparison.