A comparison of ZnMgSSe and MgS wide bandgap semiconductors used as barriers: Growth, structure and luminescence properties

Abstract

The wide bandgap alloy Zn 0.2Mg 0.8S 0.64Se 0.36 has recently been grown by molecular beam epitaxy (MBE) and been shown to be oxidation and acid resistant. This makes it attractive either as a replacement or adjunct to MgS in II–VI multilayers. In this paper we compare the structural and optical properties of MBE grown multilayer structures containing Zn 0.2Mg 0.8S 0.64Se 0.36 to those grown with the quaternary alloy replaced by MgS. Cross-sectional high-resolution transmission electron microscopy (HRTEM) and X-ray interference spectra of ZnSe/Zn 0.2Mg 0.8S 0.64Se 0.36/ZnSe multilayers show the Zn 0.2Mg 0.8S 0.64Se 0.36 layers are of good crystal quality and do not phase segregate. Layer interfaces are seen to be flat and Zn 0.2Mg 0.8S 0.64Se 0.36 does not introduce defects into the overlying ZnSe. Atomic force microscopy shows the surface of a 30 nm Zn 0.2Mg 0.8S 0.64Se 0.36 layer is atomically flat, in contrast with similar MgS layers, which show pronounced 1D surface ridges, indicating that the Zn 0.2Mg 0.8S 0.64Se 0.36 layers have not started to relax. ZnSe quantum wells grown with Zn 0.2Mg 0.8S 0.64Se 0.36 barriers show 77 K photoluminescence comparable in wavelength and intensity to ZnSe wells of similar thickness grown with MgS barriers. This has allowed us to demonstrate the use of the quaternary alloy, which resists oxidation in place of MgS in multilayer structures.