Applications of thermodynamical modeling in molecular beam epitaxy of CdxHg1-xTe |
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Authors: | T Colin T Skauli |
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Affiliation: | (1) Division for Electronics, Norwegian Defence Research Establishment, P.O. Box 25, N-2007 Kjeller, Norway |
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Abstract: | It is well known that the crystalline quality of CdxHg1-xTe grown by molecular beam epitaxy is critically dependent on the substrate temperature. The optimal growth temperature has
been identified immediately below the crossing of the Te-rich phase boundary, that is just below the temperature range where
Te precipitation occurs in the layer. It is potentially very useful to be able to predict the optimal temperature and its
variation with other growth parameters, but no general guidelines for this can be found in the literature. We have studied
experimentally the variation of the optimal growth temperature with Hg flux, Cd mole fraction and growth rate. These results
are compared with a thermodynamical model published previously by Gailliard. We find that the modeled position of the phase
boundary coincides well with the observed variations in optimal growth temperature for growth on Te-terminated surfaces, within
the uncertainties of available thermodynamical constants. We show that the optimal substrate temperature depends mainly on
the Hg flux and Cd mole fraction, while the dependence on growth rate can be neglected in practical molecular beam epitaxy
conditions. The experimental observation of optimal layer quality at the phase boundary could suggest the existence of an
adsorbed layer of Te, acting as a reservoir for Te atoms and reducing the supersaturation of the growth reaction. Simultaneous
growth on the (211)B and (100) orientations reveals a clear, although not very large, difference in optimal growth temperature
and Cd incorporation, indicating a difference in growth kinetics. This can be accounted for in the thermodynamical model by
condensation and evaporation coefficients. |
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Keywords: | Condensation and re-evaporation coefficients HgCdTe molecular beam epitaxy (MBE) Te-rich phase boundary thermodynamic prediction of optimal growth temperature |
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