ZnSxSe1 - x
Polymer and Materials Science
Wiley InterScience Backfile Collection 1832-2000
Electrical Engineering, Measurement and Control Technology
In this paper we report new results concerning the cause of impurities responsible for the Ix, and I2-peaks in photoluminescence (PL) spectra of ZnSe grown by MOVPE. An improvement in ZnSe epilayer quality is obtained by using a metal organic selenium precursor with reduced chlorine concentration. The PL spectrum of such a layer shows typical excitonic transitions, but compared with samples grown with a more contaminated source, the intensity of the Ix, and the I2 peaks decreases relative to the free exciton transition. A Gaussian fitting of the donor-bound exciton peaks taking the background of other structures into account shows that the ratio between the Ix and I2 peaks does not differ significantly between two samples. Both the decrease in donor-bound exciton transitions and the unchangeability of the ratio Ix/I2lead to the conclusion that only chlorine impurities are responsible for Ixand Ix. In order to verify the homogeneity of impurity uptake across a 2 inch wafer, we performed PL mapping of ZnSxSe1 - x layers. Mapping of a 2 inch ZnSe wafer shows that the FWHM of Ix across a wafer does not vary significantly (1.55 ± 0.21 meV). On mapping a 2 inch ZnS0.3Se0.7 wafer fabricated with H2S as the sulphur source at TD = 480°C, we found a rotational symmetric dstribution of sulphur in the layer. The sulphur content x at the centre is nearly constant. The difference in x between the centre and the boundary of a bad surface region at the edge of the wafer is less than Δx = 0.045. The FWHM of the band edge luminescence follows the same tendency across the wafer. The dependence of homogeneity on the reactor design as well as the uptake of unintentional impurities from the precursor is discussed in detail.
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