Compositional ordering in SiGe alloy thin films

Synthesis and Characterization of Nano-to Meso Scale Ordered Structures in the Si1-xGex Alloy System

“…Apart from Si(001) substrates, ordering has been reported for growth on Ge(001) substrates as well, further corroborating that the epitaxial strain does not drives the ordering process, since the sign of the strain changes for alloy growth on Ge vs. Si. 15,61,76 With all these observation and reports, it was concluded that the ordering in SiGe is metastable for the bulk of the alloy, and strictly results from surface growth kinetics occurring on the 2x1 reconstructed growth surfaces. Extensive work has been done to understand the mechanism of RS2 ordering observed in Si1-xGex alloys.…”

“…For the most part, these order parameters are consistent with the literature, although it must be noted that while many studies have shown evidence of ordering by the presence of superlattice reflections, few have accurately and correctly quantified S. Significantly higher order parameters were reported for very thin SiGe alloy films (up to S = 0.71 at 5 nm thickness) based on in situ x-ray surface diffraction measurements. 61 An order parameter of 0.64 was claimed in a standard XRD analysis of 500 nm thick Si0.5Ge0.5 films grown at 390 ºC, but details on the calculation were not provided. 79 A thorough characterization of order parameter was performed by Tischler, et al 74 , who obtained S = 0.28 for a 300 nm thick Si0.5Ge0.5 film grown on Si(001) at 400 ºC by MBE.…”

“…The process of DI water and UV-ozone exposure was repeated several times with the last step being the UV-ozone exposure. 60,61 The oxide layer was desorbed in situ at about 450 ˚C after a 5 hr prebake at 350 ˚C, resulting in a clean 2x1 reconstructed Ge surface for epitaxial growth. …”

“…72 Reported growth temperatures to foster ordering are below 550 ˚C, generally in the proximity of 400 ˚C. [10][11][12]14,15,61,74 Kuan, et al, 13 Muller, et al, 11 and LeGoues, et al, 12,72 found that the ordering is not related to substrate strain and its existence is solely dependent upon the conditions of the dynamic growth surface.…”

“…Surprisingly, only a few papers have accurately and correctly quantified the order parameter in these alloys. 61,74 In the following section we describe in detail how the order parameter was quantified for all the SiGe samples used here.…”