Controlled Interface Roughness in GaAs/AlAs Superlattices
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CONTROLLED INTERFACE ROUGHNESS IN GaAs/AlAs SUPERLATTICES WILLIAM R. MILLER, JR.,* W. 3. BOETTINGER,** W. F. TSENG,** J. PELLEGRINO," *Current Address:
AND J. COMAS** Guest Scientist at NIST, on leave from Penn State University,
Middletown, PA 17057
"**NationalInstitute of Standards
and Technology, Gaithersburg, MD 20899
ABSTRACT We report the results of our study of controlled interface roughness in low-order GaAs/AlAs superlattices. Samples were prepared using either the interrupted growth or the migration-enhanced epitaxy (MEE) technique. The samples were prepared with m atomic planes of GaAs and m atomic planes of AlAs (m x m) per modulation wavelength and repeated p times. For this study, m = 1 or 3. The samples were studied using X-ray diffraction. The interrupted growth samples both showed a split in one diffraction line indicating layers were not of integral order while the MEE samples showed no splitting, indicating integral order layers. INTRODUCTION 2 There is considerable interest in the fabrication,(1) basic physics,(M) and device applications(") of multilayer structures and superlattices. The physical properties of such entities can be strongly affected by the structure and composition of the interfaces between layers. Most theoretical work is based on the assumption of abrupt interfaces. Departures from ideal interfaces, i.e., interfacial disorder, may come from factors such as substrate roughness and variations in deposition rate.
Recently, Schuller et al.(5) introduced the concept of "controlled interface roughness" which fundamentally differs from random roughness. Controlled roughness comes from deposition of a noninteger number of atomic planes in each layer and results in an interfacial layer that consists of an AlAs/GaAs mixture that varies in a systematic manner in succeeding interfaces. The resulting diffraction pattern for controlled roughness is different than that for random roughness. In the case of random roughness, the line is broadened, but with no change in position. For controlled roughness, the line is sharp and its position altered. Using their notation, a diffraction spectrum consists of two series of peaks, denoted by n~m where n gives the order of the main reflection and ±m labels its satellites. For a 1 x 1 sample, a peak 0+1, counting from the (000) line, should coincide with the 1-1 peak, counting from the (002) peak. Since there is a noninteger number of atomic layers, the 0+1 and 1-1 lines do not coincide, but the peak near 29 = 15'C is split. Schuller et al. were able to prepare samples which showed this behavior by carefully controlling the growth rates to yield a noninteger number of atomic planes. In our work, the objective was to see whether or not this behavior occurred in loworder GaAs/AlAs superlattices prepared by (1) the interrupted growth techniques and (2) by the migration-enhanced epitaxy technique. We prepared and studied by X-ray diffraction 1 x 1 and 3 x 3 samples using both deposition modes.
Mat. Res. Soc. Symp. Proc. Vol. 230. ©1992 Materials Resea
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