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The effect of substrate misorientation on the homoepitaxial growth of cadmium telluride by organometallic vapor phase epitaxy

Posted on:1998-02-17Degree:Ph.DType:Dissertation
University:Carnegie Mellon UniversityCandidate:Yong, KijungFull Text:PDF
The goal of the research presented in this dissertation was to study the effect of substrate misorientation on the homoepitaxial growth of CdTe by OMVPE.; Vicinal CdTe(100) misoriented toward (111){dollar}rmsb{lcub}Te{rcub}{dollar} by up to 8{dollar}spcirc{dollar} have stable stepped surface structures consisting of a series of terraces separated by regularly spaced steps. As misorientation increased, the step density increased.; Surface reaction studies of dimethylcadmium (DMCd) and diisopropyltellurium (DIPTe) on CdTe revealed that DMCd and DIPTe were desorbed molecularly instead of decomposing on the surface. Most previously proposed mechanisms for CdTe OMVPE growth assumed that DMCd and DIPTe dissociatively and irreversibly adsorbed on the surface. Our direct surface reaction studies, however, indicated that the mechanism should include the reversible adsorption step of organometallic precursors.; Growth studies showed that the CdTe growth rate increased as misorientation angle increased from 0{dollar}spcirc{dollar} to 8{dollar}spcirc.{dollar} The overall activation energy of the growth was 14.5 {dollar}pm{dollar} 1.0 kcal/mol for all misoriented substrates. The CdTe growth on CdTe(100) and CdTe(100)4{dollar}rmspcircto(111)sb{lcub}Te{rcub}{dollar} showed a sublinear dependence of the growth rate on the partial pressures of DMCd and DIPTe for both substrates.; The film morphology was strongly dependent on the substrate misorientation. The formation of a low angle ({dollar}{lcub}sim{rcub}8spcirc){dollar} of pyramidal hillock was observed on CdTe(100). A cross-sectional TEM of CdTe film on singular surface revealed that there is no relationship between pyramid hillocks and crystalline defects in the epilayers, indicating that the formation of hillocks was due to intrinsic instability of the growth on a singular surface. A smooth morphology was observed on the misorientation of 4{dollar}spcirc{dollar} and at higher misorientation angle, the film morphology was degraded.; A growth model was proposed for CdTe OMVPE. This model takes nucleation and step flow on surfaces into considerations. Monte Carlo simulation results showed a good consistency with growth experimental results of CdTe. The transition of film morphology from hillock formation to smooth was related with the transition of growth mode from nucleation to step flow. The formation hillocks on the singular surface was related with an energy barrier at step edges for the downward diffusion of adatoms to the next terrace.
Keywords/Search Tags:Misorientation, Growth, Surface, Cdte
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