Reducing the defect density in MBE-ZnSeIII–V heterostructures

The defect densities that are observed in 1 μm ZnSe films grown by molecular beam epitaxy on various III–V buffer layers are compared. Cathodoluminescence (CL) imaging has been used to provide a rapid and non-destructive method of characterizing the defect densities and was found to be in agreement with both etch pit density and transmission electron microscopy characterizations. We also examined the defect density of ZnSe epilayers grown on relaxed buffer layers of (In,Ga)P (lattice-matched to ZnSe) with the phosphide surface capped with eight monolayers of GaAs exhibiting various surface reconstructions. In this manner, the ZnSe GaAs surface chemistry is maintained while simultaneously achieving a lattice-matched buffer layer to ZnSe. Films grown without special nucleation precautions on c (4 × 4)-reconstructed GaAs were typically found to result in defect densities larger than 10 7 cm −2 . Using a Zn pre-exposure on (2 × 4)-reconstructed GaAs, the defect densities were decreased by over an order of magnitude. In this paper, the microstructural and optical properties of ZnSe on phosphide-containing III–V buffer layers will be described and contrasted to the more conventional ZnSe GaAs heterostructure, using atomic force microscopy and CL.