IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Semiconductors Tuesday Sessions
       Session SC-TuM

Paper SC-TuM3
Nanometer-scale Studies of Phase Separation in Compound Semiconductor Alloys

Tuesday, October 30, 2001, 9:00 am, Room 124

Session: Semiconductor Interfaces and Thin Films
Presenter: B. Shin, University of Michigan
Authors: B. Shin, University of Michigan
A. Lin, University of Michigan
K. Lappo, University of Michigan
R.S. Goldman, University of Michigan
M.C. Hanna, National Renewable Energy Laboratory
S. Francoeur, National Renewable Energy Laboratory
A.G. Norman, National Renewable Energy Laboratory
A. Mascarenhas, National Renewable Energy Laboratory
Correspondent: Click to Email
Thin films of compound semiconductor alloys can be grown with a wide range of band gap energies and lattice constants, useful for the development of novel electronic and optoelectronic devices. In most of these systems, growth conditions have been reported for which phase separation occurs. Yet, the thermodynamic versus kinetic origin of phase separation, as well as the experimental conditions for determining the presence of phase separation has been the subject of debate for nearly 20 years.@footnote 1,2@ In thin films of compound semiconductor alloys, both the difference in binary bond lengths and the film/substrate misfit are expected to play a significant role in the initiation of alloy phase separation. In this work, we have examined phase separation in the misfit-free InAlAs/InP system using ultra-high vacuum cross-sectional scanning tunneling microscopy (XSTM) and x-ray reciprocal space mapping. For p-doped thin InAlAs layers, XSTM reveals the presence of isotropic non-uniformities which consist of nanometer-sized clusters. For thicker, undoped InAlAs layers, longer wavelength quasi-periodic modulations perpendicular to the growth direction are apparent. These lateral modulations are observed in both topographic and conductance XSTM images, suggesting that they are due to a combination of compositional and strain variations. A signature of these modulations is also apparent in x-ray reciprocal space maps. Interestingly, the modulation wavelengths increase with film thickness and are notably lower than those reported for similar films grown at higher temperatures.@footnote 3@ Together, these results suggest that phase separation is a thermally activated kinetic process which may be significantly affected by the presence of impurities such as dopants. @FootnoteText@@footnote 1@G. B. Stringfellow, J. Cryst. Growth 65, 454 (1983). @footnote 2@A. Zunger and S. Mahajan, in Handbook on Semiconductors (North-Holland, Amsterdam, 1994), Vol. 3, p. 1399. @footnote 3@H. K. Cho et al, Mat. Sci. Eng. B 64, 174 (1999).