Controlling (In,Ga)As quantum structures on high index GaAs surfaces
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JJ1.8.1/KK1.8.1/U1.8.1
Controlling (In,Ga)As quantum structures on high index GaAs surfaces Sh. Seydmohamadi, H. Wen, Zh. M. Wang, and G. J. Salamo Department of Physics, University of Arkansas, Fayetteville, Arkansas, 72701, U. S. A.
Abstract We investigate the formation of (In,Ga)As self assembled quantum structures grown on different orientations of a GaAs substrate along one side of the stereographic triangle between (100) and (111)A surfaces. The samples were grown by Molecular Beam Epitaxy, monitored by Reflection High-Energy Electron Diffraction during the growth and characterized by in-situ Scanning Tunneling Microscopy and Atomic Force Microscopy. A systematic transition from zero dimensional (In,Ga)As quantum dots to one dimensional quantum wires was observed as the substrate was varied along the side of the triangle within 25o miscut from the (100) toward (111)A, which includes several high index surfaces. We propose an explanation for the role of the substrate in determining the type of the nanostructure that is formed. Introduction Generally, high index semiconductor substrates have the potential to act as templates for the growth of quantum structures. This potential is based on the unique surface morphology of high index surfaces that can influence the size, shape, uniformity, and location of self-assembled nanostructures [1,2,3]. For example, experiments already demonstrate that the orientation of the substrate surface can play an important role in the formation of different types of (In,Ga)As heteroepitaxial quantum structures grown on GaAs [4,5,6]. In this work, we investigate the transformation of (In,Ga)As nanostructures along one side of the stereographic triangle between (100) and (111)A, and explain the role of the substrate based on stability of the high index {11 5 2} surface. Interestingly we observe the formation of different quantum structures just by changing the misorientation angle from (100) within 25o toward the (111)A surface. The surfaces studied here by Molecular Beam Epitaxy (MBE), in-situ Scanning Tunneling Microscopy (STM) and Atomic Force Microscopy (AFM) include the (100), (711)A, (511)A, (411)A and (311)A. Fig. 1 is a bulk lattice viewed along the [01-1] direction, representing each of the surfaces investigated, by the degree of miscut from the (100) template. For the same coverage of (In,Ga)As, a systematic transition from zero dimensional (In,Ga)As quantum dots (QDs) to one dimensional quantum wires (QWRs) was observed as the substrate was varied along one side of the triangle between (100) and (111)A. While (In,Ga)As QDs form on GaAs (100) and (711)A surfaces, elongated (In,Ga)As QDs formed on the GaAs (511)A surface and QWRs on GaAs (311)A and (411)A surfaces. An explanation for the different confined structures observed for substrates along one side of the stereographic triangle is presented.
JJ1.8.2/KK1.8.2/U1.8.2
(100) (711) (11.4o) (511) (15.8o) (411) (19.5o)
[100]
(311) (25.2o)
[01-1] [011]
Ga (111) (54.7o)
As
Figure 1: Schematic cross section of the GaAs
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