The effect of substrate misorientation angle on the band gap energies of II-VI compound semiconductors grown by molecular beam epitaxy

The effect of substrate misorientation angle (SMA) on the band gap energies of II-VI compound semiconductor epilayers, Zn1-xMgxSe, Zn1-xMnxSe, ZnSe1-x Tex, Zn1-xCdxSe and ZnSe1-xSx, was studied by optical spectroscopy. The ban d gap energies were found to increase with substrate misorientation (tilted ) angle for Zn1-xMgxSe, ZnSe1-xTex, Zn1-xCdxSe and ZnSe1-xSx epilayers. Whi le for the Zn1-xMnxSe epilayers, the band gag energies decrease with SMA. B oth the decrease (for Zn1-xMnxSe epilayers) and increase (for the other epi layers) in band gap energy are attributed to the increasing incorporation o f smaller ions as the SMA is increased. The dependence of the energy gap on the SMA is almost linear for ZnSe1-xTex and Zn1-xMnxSe epilayers. For Zn1- xMxSe and Zn1-xCdxSe epilayers, the energy gap increases abruptly at a smal l tilt angle, then becomes insensitive to the SMA at a tilt angle larger th an 10 degrees. In the case of the ZnSe1-xSx epilayer, the situation is reve rsed. At smalt angles the SMA has little influence on the band gay energy. At a SMA larger than 10 degrees, the band gap energy increases suddenly. Th e sudden increase with SMA at a large tilt angle results from the abrupt in crease in kink density which is a function of the square of the tilt angle. The energy difference between the energy gap of an epilayer grown on [100] substrate and an epilayer grown on [100] substrate with 15 degrees tilt to ward [010] is largest (18 meV) for Zn1-xMxSe epilayers. For Zn1-xMnxSe, ZnS e1-xSx and ZnSe1-xTex epilayers, the energy differences are about 5 meV.