Growth of MgTe and Cd 1− xMg xTe thin films by molecular beam epitaxy

Abstract

We report on the growth of the compound semiconductor MgTe as well as the ternary alloy Cd 1− x Mg x Te by molecular beam epitaxy. This is to our knowledge the first time that this material has been grown by any epitaxial technique. Bulk MgTe, which is hygroscopic, has a band gap of 3.0 eV and crystallizes usually in the wurtzite structure. Pseudomorphic films were grown on zincblende CdTe substrates for a MgTe thickness below a critical layer thickness of approximately 500 nm. In addition, Cd 1- x Mg x Te epilayers were grown with a Mg concentration between 0 and 68%, which corresponds to a band gap between 1.5 and 2.5 eV at room temperature. The crystalline quality of the layers is comparable to CdTe thin films as long as they are fully strained. The lattice constant of zincblende MgTe is slightly smaller than that of CdTe, and the lattice mismatch is as low as 0.7%. In addition highly n-type CdMgTe layers were fabricated by bromine doping. The tunability of the band gap as well as the rather good lattice match with CdTe makes the material interesting for optoelectronic device applications for the entire visible range.