Photo-metal organic vapor phase epitaxy: A low temperature method for the growth of Cd<i>x</i>Hg1−<i>x</i>Te

Abstract

A new epitaxial growth technique, photo-metal organic vapor phase epitaxy (photo-MOVPE), is described for the growth of CdxHg1−xTe (CMT). Ultraviolet radiation is used to decompose the metal-organics, diethyl-telluride (Et2Te) and dimethyl-cadmium (Me2Cd) on the substrate surface. Epitaxial HgTe can be grown at relatively low temperatures (200–300 °C) by a surface photosensitization reaction. However, the growth of CMT is only epitaxial if an inert carrier gas (He) is used instead of H2. These results are described in terms of suppression of vapor phase nucleation while allowing surface nucleation to occur. Vapor phase nucleation results in the deposition of fine particles of CMT and can totally disrupt epitaxial growth. The growth rate dependence of CMT on CdTe substrate orientation is considered and compared with HgTe growth rates on the same orientations. These results show that surface kinetics can dominate the growth process, making it insensitive to vapor concentrations. Secondary ion mass spectrometry (SIMS) profiles through a CMT layer, grown at 250 °C, for the major elements, Cd, Hg, and Te, show an abrupt interface between the substrate and layer of less than 400 Å. Carbon impurity profiles through HgTe layers show that using the inert gas, carbon incorporation is no greater than for H2 carrier gas. It is shown that carbon is not a major contaminant in the epitaxial HgTe and CMT layers, but may still be a problem at lower concentrations.