Investigations of ZnSe based laser structures on ZnSe substrates by high resolution x-ray diffraction

The structural quality of homoepitaxially grown ZnSe based layers depends s ensitively on the ZnSe substrate preparation prior to the growth. In this p aper the consequences of an in situ hydrogen plasma cleaning of ZnSe substr ates to the crystalline quality of II-VI based laser structures are discuss ed. The crystalline properties of the resulting laser structures are compar ed with those of homoepitaxially grown structures on non-hydrogen cleaned s ubstrates as well as with the characteristics of heteroepitaxially grown la sers on GaAs. The samples were grown by molecular beam epitaxy and characte rized by high-resolution x-ray diffraction. Remarkable differences in the s train state of the homoepitaxially grown samples are observed. While the st ructures grown on hydrogen cleaned ZnSe substrates are pseudomorphic, layer s of comparable thickness and lattice mismatch on non-hydrogen cleaned subs trates show clear strain relaxation. Triple axis (004) rocking curves revea l distinct differences between the three sample types investigated. Accordi ng to these measurements, the in situ hydrogen plasma cleaning of ZnSe subs trates results in a drastic improvement of crystalline perfection of the ho moepitaxial laser structures. However, even the defect density of the optim ized homoepitaxial samples exceeds that of heteroepitaxial reference lasers by two orders of magnitude as estimated from the diffuse scattered intensi ty.