Selective Area Epitaxy of CdTe on Nanopatterned Substrates

2014-04-15T00:00:00Z (GMT) by Stephen D. Fahey
HgCdTe/Si devices can potentially be significantly improved by the use of nanopatterned substrate structures on Si to control point and extended crystal defects. This thesis contains an exploration of one such nanopatterned substrate structure on Si. The results include the demonstration of selective area molecular beam epitaxy of single-crystalline CdTe against SixNy , SiOx, and carbon mask materials; as well as the coalescence of CdTe grown in selective areas, against SixNy mask. The coalescence is shown to have an in-plane asymmetry related to step-flow growth of CdTe(211). The coalesced film is also shown to have small surface corrugation, related to the initial separation of neighboring seed islands. This thesis further reports on the feasibility of a patterned 500nm-pitch SixNy and CdTe interface structure to reduce the dislocation density intersecting the final surface of CdTe/ZnTe/Si(211) grown by molecular beam epitaxy. It is found that the patterned substrate structure tested in this thesis work is likely insufficient to reach that goal, as the strongest x-ray diffraction peak from the patterned samples reported here is 7 times wider, and so implies the dislocation density is higher than unpatterned growth of CdTe/ZnTe/Si(211) under identical growth conditions. To achieve a comparative reduction in dislocation density on a patterned substrate, the fabrication of smaller and closer seeding islands is recommended.