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In Situ Spectroscopic Ellipsometry for Monitoring and Control of HgCdTe Heterostructures Grown by Molecular Beam Epitaxy

Published online by Cambridge University Press:  10 February 2011

L. A. Almeida ,
M. J. Bevan ,
W. M. Duncan  and
H. D. Shih
L. A. Almeida
Affiliation:
Microphysics Laboratory, Physics Department, University of Illinois at Chicago, Chicago, IL 60607
M. J. Bevan
Affiliation:
Texas Instruments Incorporated, Corporate Research & Development, P.O. Box 655936, MS 150, Dallas, TX 75265
W. M. Duncan
Affiliation:
Texas Instruments Incorporated, Corporate Research & Development, P.O. Box 655936, MS 150, Dallas, TX 75265
H. D. Shih
Affiliation:
Texas Instruments Incorporated, Corporate Research & Development, P.O. Box 655936, MS 150, Dallas, TX 75265
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Abstract

A major advantage of vapor phase epitaxial growth techniques is their flexibility to produce Hg1−xCdxTe layers with difFerent compositions from one run to the next, as well as the flexibility to produce compositional heterostructures of Hg1−xCdxTe in one process step. To take full advantage of this flexibility, reliable, automated control must be introduced. To this end, a phase-modulated spectroscopie ellipsometer (SE) has been implemented for use as a contactless wafer state sensor. In this work SE was used to monitor in real-time the stoichiometry of epitaxial Hg1–4CdxTe during growth by molecular beam epitaxy (MBE). SE has provided valuable information about the MBE growth process, by revealing even small fluctuations in x (± 0.002). In particular, SE has measured the compositional profiles of both LWIR/MWIR and MWIR/LWIR interfaces. Distinct profiles were revealed for interfaces created by abrupt changes in the CdTe effusion cell set-point and for interfaces created by ramping the cell temperature linearly. Ramping results in a smoothly graded interface, whose thickness may be pre-determined, though typically 2000 Å. An abrupt set-point change results in a sharper transition (∼300 Å) followed by oscillations in composition associated with the settling time of the cell (∼1500 Å). The thickness of a CdTe passivation layer grown on a LWTR layer was determined. The current status of the SE will be reported through other illustrative examples which demonstrate its utility as a diagnostic tool and as a sensor for realtime, feed-back control of the MBE process.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 450: Symposium O – Infrared Applications of Semiconductors , 1996 , 269
Copyright
Copyright © Materials Research Society 1997

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References

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