Defect Structures in Heteroepitaxial InAs/GaAs and GaAs/InAs Grown by Atomic Layer Molecular Beam Epitaxy
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DEFECT STRUCTURES IN HETEROEPITAXIAL InAs/GaAs AND GaAs/InAs GROWN BY ATOMIC LAYER MOLECULAR BEAM EPITAXY S.I.MOLINA, G.ARAGON AND R.GARCIA Departamento de Quimica InorgAnica, Puerto Real (Cddiz). Spain.
Universidad de Cfdiz, Apdo.
40
11510
ABSTRACT A Transmission Electron Microscopy (TEM) study on ALMBE grown InAs/GaAs(001) is presented. The density and the types of defects contained in InAs and GaAs layers are clearly different. A relation between the planar defects in these layers and the compressive and extensive nature of the growth for each layer is found. Atomic Layer Molecular Beam Epitaxy (ALMBE) grown InAs layers possess a better quality of defects than other InAs layers grown on GaAs (001) by conventional MBE. Several ways of nucleation are presented as possible for explaining the existence of the different defects found in the studied heterostructure.
INTRODUCTION The heteroepitaxial system InAs/GaAs (001) has a very high lattice mismatch (7.2%). Such a high lattice mismatch probably leads to an epitaxial growth with very strained layers and with a great density of dislocations [1]. The mechanism of relaxation of a strained layer depends of the elastic properties of the substrate and the epilayer, and of the conditions and the method of growth [2]. The most advantageous situation for a highly mismatched lattice, e.g. InAs/GaAs, corresponds to the case in which all the defects are located near the interface [3]. It would be useful to find the conditions of growth which lead to the mentioned situation for a heteroepitaxial system InAs/GaAs. A study by TEM of double heterostructures InAs/GaAs grown by ALMBE is presented in this work. This type of growth, ALMBE, presents some promising perspectives as a growth technique for InAs/GaAs so that some successful growth of this kind have already been reached [4]. The distribution and the types of defects in the layers of GaAs and InAs are characterized. The differences observed in the several layers are correlated with the compressive and extensive nature of the growth for each layer. Also, the possible ways of nucleation of the different defects are studied.
EXPERIMENTAL TEM studies have been carried out on several specimens containing InAs/GaAs and GaAs/InAs interfaces. The scheme of growth for these specimens is shown in figure I. A number of cross-sections were prepared for TEM study. Two transmission electronic microscopes were utilized, a JEOL 2000 EX, for High Resolution Electron Microscopy (HREM) study, and a JEOL 1200 EX, for contrast diffraction work.
Mat. Res. Soc. Symp. Proc. Vol. 262. 01992 Materials Research Society
164
RESULTS a smaller and InAs(2) layers possess The InAs(1) dislocations than the GaAs(2) layer as can be clearly seen in The quantity of planar defects is very low in the InAs layers, in InAs(1). The number of planar defects measured in GaAs(2) is in the InAs layers.
number of figure II. especially higher than
Fig. I Schematic representation of the studied heteroepitaxial system
The knowledge of the distribution of defects
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