Dependence of source gas mole ratio on crystalline quality of ZnSe layers grown on (100) ZnSe substrates by atmospheric pressure metalorganic vapor phase epitaxy

Abstract

Abstract Single crystalline layers of undoped ZnSe have been grown on (100) ZnSe substrates at 250°C by atmospheric pressure metalorganic vapor phase epitaxy (MOVPE) using dimethylzinc (DMZ) and hydrogen selenide (H 2 Se). The surface morphologies, observed by a Nomarski phase contrast interference microscope, depend on the growth conditions, particularly the source gas mole ratio η M ( η M =[Se]/[Zn]). The surface morphologies of homoepilayers grown with η M of more than 15 are very rough like polycrystals. However, these layers have the best crystalline quality as determined by a double crystal X-ray diffraction spectrometer (the full width at half maximum (FWHM) of (400) diffraction is 33 arc sec). The surface morphologies of layers grown at values of η M between 3 and 15 are excellent as well as those of heteroepilayers (GaAs substrates are used). On the other hand, the crystalline quality becomes worse by reducing η M . The photoluminescence (PL) spectra at 4.2 K exhibit strong and well-resolved band-edge emissions from the donor bound exciton (hereafter called I x ) and the free exciton (hereafter called E x ) only for the low mole ratio (η M x is 0.8 meV which is sharper than that of heteroepilayers. However, the intensity of emissions from deep levels (deep emissions) of homoepilayers measured at 77 K is several times stronger than that of heteroepilayers. In the region of high mole ratio (η M >10), the PL spectra at 4.2 K show two broad lines: I x and the unknown I v (probably donor bound exciton). And the intensity of I x reduces two orders by decreasing the mole ratio from 20 to 3. This indicates that the concentration of donor decreases for the Se-rich condition. From the investigation of PL measurements, the origin of deep emissions is considered to be caused by complexes of Zn vacancies and impurities from the source gases. The dependences of η M on the quality of homoepilayers observed in this work are quite different from those in heteroepilayers reported previously.