Vapor phase epitaxial growth and characterization of ZnS layer on GaAs substrate for LED application

Abstract

Good crystalline quality epitaxial layers of ZnS, having resistivities as low as 0.2-0.02 Ω cm, have been prepared on GaAs substrates at 500–700°C from a ZnS powder source, using an open tube system under hydrogen flow. The carrier concentrations of the layers are (0.4–5)X10 18 cm -3, depending on the growth temperature, and the room temperature electron mobilities are 40–90 cm 2/V·s, typically 50–70 cm 2/V·s. So-called green and blue copper emissions are seen in the room temperature photoluminescence spectra of the layers grown at low substrate temperatures, while the SA emission is seen for the layers grown at high substrate temperatures. These photoluminescence data are supported by EPMA and SIMS impurity analyses. The trap level with an activation energy of 0.41 eV was found, in the layers grown at high temperatures, by the transient thermoluminescence method developed by Nakazawa. This level is likely to be the same level as found by Klasens in ZnS: Cu,Ga phosphors. Most of these results, i.e. low resistivity, the SA emission and the 0.41 eV trap level, seem to be related to Ga impurities originating from the substrate, especially at high substrate temperatures, as revealed by the analyses.