Dislocation-induced spatial alignment of self-assembled InAs/GaAs quantum dots
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Dislocation-induced spatial alignment of self-assembled InAs/GaAs quantum dots H. S. Lee, J. Y. Lee, T. W. Kim1, Y. J. Park2 Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, 373-1 Guseong-dong, Yuseong-gu, Daejeon 305-701, Korea 1 Department of Physics, Kwangwoon University, 447-1 Wolgye-dong, Nowoon-gu, Seoul 139701, Korea 2 Semiconductor Materials Laboratory, Nano Device Research Centre, Korea Institute of Science and Technology (KIST), P.O.Box 131, Cheongryang, Seoul 130-650, Korea ABSTRACT We have studied the alignment of self-assembled InAs quantum dots (QDs) grown by molecular beam epitaxy using misfit dislocations generated due to the strained InxGa1-xAs/GaAs superlattice system. Structural characteristics of aligned SAQDs have been investigated by using atomic force microscopy (AFM) and transmission electron microscopy (TEM) measurements. AFM and TEM images showed that vertical stacked InAs QD arrays were aligned along direction on the controlled strained layer. The anisotropic alignments along the [110] and [ 110 ] directions are closely related with the anisotropy of strain-relief for both directions, which affect the anisotropic diffusivity of indium adatoms on the strained superlattice layer. The strong alignment appears on the highly strained layer. These results indicate that aligned InAs quantum dots formed by changing the periods of strained superlattice hold promise for potential applications in nanoelectronic devices, such as single electron tunneling devices.
INTRODUCTION Studies concerning microstructural and optical properties of self-assembled quantum dots (SAQDs) by using Stranski-Krastanow (S-K) growth mode have been widely done due to potential applications to optoelectronic devices, such as QD laser [1], optical memory [2], and infrared photodetectors [3]. Since microstructural properties of SAQDs can significantly affect their electrical and optical properties [4], studies on microstructural properties of SAQDs must be preceded before understanding of operation of optoelectronic devices based on quantum dot structures. The control of self-assembled properties in InAs/GaAs quantum dot (QD) is of great importance [5, 6]. However, it is difficult to control the size distribution and the generation site of SAQDs. Selective positioning of self-assembled QDs can be performed through patterning related technique such as e-beam and scanning tunneling microscope (STM) lithography [7, 8]. The use of vicinal substrate and high Miller indices surface provide the selective position of QD formation [9]. The positioning of QDs in V-grooved region or on ridges was obtained by using the patterned substrate [10]. On the other hand, misfit dislocations having strain fields can affect the formation of QDs since misfit dislocations become a strong source of elastic strain [11]. The alignment of self-assembled InAs QDs by using the strained superlattice system has been demonstrated [12]. Therefore, since it does not use any complicated pre-process s
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