Influence of gas flow stoichiometry on the luminescence of organometallic-vapor-phase-grown ZnxCd1−xSe epilayers

Abstract

Zn x Cd 1−x Se epilayers were grown by organometallic vapor phase epitaxy using various VI/II flow ratios at a temperature of 420 °C. Cathodoluminescence (CL) spectroscopy and imaging were used to study their luminescent properties. Both near-band gap emissions (NBE) and deep-level emissions (DLE) were found in the CL spectra. We found that the width of the NBE peak and the intensity of the DLE relative peak to that of NBE increase with an increase in the VI/II flow ratio. Both effects are traced to the presence of pyramidal growth hillocks on the surface of the epilayer and to their increased density at high VI/II ratios. Monochromatic CL images show that there are two kinds of luminescent centers contributing to the NBE. The one that emits at slightly lower energies is only found, together with the DLE centers, within the growth hillocks. The one that emits at a slightly higher energy is found from surrounding areas. The concomitant appearance of DLE centers and low energy NBE centers shows that they share a common origin. Excitation intensity dependence of the photoluminescence of the NBE centers identifies as donor–acceptor-pair recombinations.