Homogeneity of ZnSSe/ZnSe multiquantum wells grown by metalorganic vapour phase epitaxy

Abstract

The ZnS x Se 1- x (0⩽ x⩽1) layers and multiquantum well structures studied here were grown in an atmospheric or in a low-pressure metalorganic vapour phase epitaxy (MOVPE) reactor, respectively. For industrial device production, an excellent homogeneity across the whole wafer is required, so both reactors are equipped with rotating susceptors for two-inch wafers. X-ray diffraction measurements of optimized multiquantum well structures grown with diethylsulphur (DES) in the atmospheric-pressure reactor show very good structural properties and high reproducibility of the layer sequence indicated by sharp satellite peaks and “pendellösung” fringes. Also the near-band-edge photoluminescence (PL) spectrum hints on the excellent layer quality by sharp PL peaks (FWHM= 2.6 meV). The homogeneity of a multiquantum well structure across a two-inch wafer was determined from the local dependence of the PL blue-shift across the wafer. At the edge of the sample grown with H 2S the blue-shift increases, which can be explained by an increased sulphur content or a lower thickness owing to a decreased growth rate. However, Raman measurements taken at samples grown with DES show that the sulphur content is very homogeneous laterally, whereas the variation is much larger in samples grown with H 2S. Homogeneity tests for ZnSSe grown with DES under low pressure or atmospheric pressure show no significant difference. Nevertheless, with H 2S as a sulphur source, the gas phase depletion was reduced at low pressure. With increased gas flow velocity, both the sulphur content and the growth rate homogeneity were improved.