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Compositionally Modulated Structures Studied by in Situ Scanning Tunneling Microscopy

Published online by Cambridge University Press:  17 March 2011

Chris A. Pearson ,
Catalina Dorin ,
Joanna Mirecki Millunchick ,
Yunqing Chen  and
Brad G. Orr
Chris A. Pearson
Affiliation:
Department of Computer Science, Engineering Science and Physics, University of Michigan-Flint, Flint, MI 48502
Catalina Dorin
Affiliation:
Department of Materials Science and Engineering, University of Michigan, Ann Arbor, MI 48109
Joanna Mirecki Millunchick
Affiliation:
Department of Materials Science and Engineering, University of Michigan, Ann Arbor, MI 48109
Yunqing Chen
Affiliation:
The Harrison M. Randall Laboratory, University of Michigan, Ann Arbor, MI 48109
Brad G. Orr
Affiliation:
The Harrison M. Randall Laboratory, University of Michigan, Ann Arbor, MI 48109
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Abstract

Two different short period superlattice (SPS) structures with nominally equivalent lattice mismatch, InAs/AlAs and InAs/GaAs are examined using in situ scanning tunneling microscopy (STM). Depending upon the growth conditions, the composition of the InAs/AlAs SPS structure can be either homogeneous or modulated in the lateral direction. Distinct periodic structures are clearly visible in images of the modulated SPS while no periodicity is observed in the homogeneous SPS. For a 30 period SPS consisting of 2 monolayers of AlAs and 2 monolayers of InAs we observe structures 20 nm in size with an average spacing of ∼25 nm in orthogonal directions, which is approximately the same length scale as the composition modulation. Despite the nominally equivalent lattice mismatch, the InAs/GaAs SPS structures are quite different. Some degree of modulation is always observed in these structures. Homogeneous structures are not observed. For the modulated SPS structures, scanning tunneling spectroscopy can be used to characterize the chemical profile.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 696: Symposium N – Current Issues in Heteroepitaxial Growth--Stress Relaxation and Self Assembly , 2001 , N8.9
Copyright
Copyright © Materials Research Society 2002

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