High temperature growth of ZnS and ZnMgS by molecular beam epitaxy under high sulfur beam pressure

Abstract

ZnS and ZnMgS layers have been grown onto GaP substrates by molecular beam epitaxy (MBE). The key parameters of the growth are a high substrate temperature and a high sulfur (S) beam pressure. The S beam pressure was typically 1×10−2 Pa, which was more than one order of magnitude larger than in conventional MBE of ZnS. Using the high S beam pressure, large ZnS growth rate of 0.3–1.0 μm/h could be obtained even at 490 °C. The growth rate was limited by the Zn supply. Optimization of the S beam pressure reduces the full width at half maximum (FWHM) of the (400) double-crystal x-ray rocking curve (DCXRC). For a 2.1-μm-thick ZnS layer the width can be reduced to 400 arcsec. The low temperature photoluminescence (PL) spectra show sharp excitonic emissions including the free exciton emission. ZnMgS layers were grown onto ZnS buffer layers. The ZnMgS layers as well show good crystal and optical qualities. The FWHM of DCXRC of the 1.5-μm-thick Zn0.83Mg0.17S layer is 650 arcsec, which is comparable to the FWHM of a ZnS layer of similar thickness. The low temperature PL of the ZnMgS layer is dominated by a strong excitonic emission. The band gap of Zn1−xMgxS is estimated from reflection spectra. For x=0.20, the band gap is 3.974 eV.