Single crystalline layers of undoped ZnSe have been on (100) ZnSe substrates by atmospheric pressure MOVPE using dimethylzinc (DMZ) and hydrogen selenide (H2Se). The layers are typically 6 μm thick and the surface morphologies, measured by Nomarski phase contrast interference microscopy, appear superior to those of ZnSe layers grown on GaAs subrates. The photoluminescence (PL) spectra at 4.2 K exhibit strong band edge PL peak dominated by donor bound exciton (DBE) and free exciton (FE) emissions. The full width at half maximum (FWHM) of DBE is 0.8 meV and sharper than that of layers grown on GaAs substrates. However, the intensity of the self-activated (SA) PL of the homoepilayer measured at 77 K is several times more intense than that of heteroepilayers. From the investigations on the gas source molar ratio, it is inferred that the reason for this is that Zn vacancies diffuse from the substrate into the layer even at a growth temperature as low as 250°C. The characterization of the crystallographic properties by double X-ray diffraction rocking curves shows that the crystalline quality of the homoepilayers is drastically improved by heat treatment (300-650°C) of the ZnSe substrate under hydrogen atmosphere in the reactor before growth. The FWHM of the (400) diffraction of the homoepitaxial layer grown under the optimum conditions is 77 arc sec and this value shows that the ZnSe layer has the highest crystalline quality which has ever been obtained by any growth technique. © 1988.
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