Date of Award
Doctor of Philosophy
Physics and Astronomy
The quality and thermal stability of (1,1,1) oriented HgTe-CdTe, Hg[subscript]1 - xMn[subscript] xTe-CdTe, Hg[subscript]1 - xZn[subscript] xTe-CdTe, and Hg[subscript]1 - xCd[subscript] xTe-CdTe superlattices (SLs) and (0,0,1) oriented CdTe-ZnTe SLs, grown by molecular beam epitaxy, are investigated using x-ray diffraction. Two significant research contributions are achieved in this investigation. First, SL interdiffusion is investigated using an in-situ x-ray diffraction method, which represents a fundamentally different approach compared to the quenched sample method. Second, the step model structure factor, which includes angle dependent atomic scattering factors, atom vacancies, and interface transition regions, is applied to strained layer CdTe-ZnTe SLs;Zero level precession films reveal that all SL components are epitaxially related and that twinning is prevalent in (1,1,1) HgTe-CdTe SLs. All SL periods are found to be incommensurate with the average constituent lattice. The measured periods are within one average constituent cell length of the expected values, with differences as large as three constituent cell lengths observed. Calculated Scherrer lengths indicate that approximately 3 to 40 of ~250 SL unit cells coherently diffract along the growth direction. Inhomogeneous film growth is common, with lateral period variations as large as 16% over a 9 mm distance observed. Observed trends in the satellite peak widths of CdTe-ZnTe correspond to period variations ranging from 5% to 10%. Correlating peak positions with step model information, constituent layer strains of the CdTe-ZnTe SLs, which are approximately one-fourth of the theoretically predicted values, are observed along the growth direction;The thermal stability of the Hg-based SLs is assessed from in-situ interdiffusion measurements. The interdiffusion process is nonlinear. Incorporation of either Cd or Mn into the HgTe constituent layers significantly enhance the SL thermal stability. Growth interdiffusion is observed in two thick (6.2 [mu] and 6.6 [mu]) HgTe-CdTe SLs, by probing each sample with four radiation wavelengths having penetration depths ranging from 6 to 26 microns. ftn[superscript]1DOE Report IS-T-1250. This work was performed under contract No. W-7405-Eng-82 with the U.S. Department of Energy.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
Ralph David Knox
Knox, Ralph David, "X-ray diffraction characterization of the quality and thermal stability of II-VI semiconductor superlattices " (1988). Retrospective Theses and Dissertations. 8783.