Growth and characterization of CdTe/Si heterostructures - effect of substrate orientation

Transmission electron microscopy and small-probe microanalysis have been us ed to compare the microstructure and compositional profiles of CdTe/Si hete rostructures grown by molecular beam epitaxy on (001), (211) and (111) sili con substrates. Overall, our results have demonstrated that the final CdTe growth orientation is determined by careful preparation of the Si substrate surface, the nature of the interfacial layer, and the initial phase nuclea tion. Initial studies confirmed that growth on (001) was problematical, not only because of the large lattice mismatch between materials (approximatel y 19%), but also because the double-domain reconstruction of the Si substra te surface degraded epilayer quality. Growth of high quality, domain-free C dTe(111)B was achieved by offcutting the substrate with respect to the [110 ] surface direction, with an additional rotation about [110]. Alternatively , with intermediary buffer layers of Ge(001), perfect a/2[110] Lomer edge d islocations accommodated the misfit at the CdTe/Ge interface, and the (001) orientation of the Si substrate was retained during CdTe growth. For (211) -oriented substrates a very thin (approximately 2 nm) buffer layer of ZnTe prior to CdTe deposition was sufficient to maintain the substrate orientati on, although Zn diffusion was often observed during subsequent annealing. T he growth of Cd1-xZnxTe(211)B (with x similar to 2-4%) with intermediary Cd Te buffer layers then provided substrates which were suitably lattice-match ed for growth of HgCdTe, Finally, large-area, domain-free CdTe(111)B was ac hieved using As-passivated Si(111) substrates and thin (approximately 50 nm ) ZnTe buffer layers. (C) 2000 Elsevier Science S.A. All rights reserved.