Structural investigation of InAs/InGaAs/InP nanostructures: origin and stability of nanowires
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Structural investigation of InAs/InGaAs/InP nanostructures: origin and stability of nanowires. L.Nieto1, H.R.Gutiérrez2, J.R.R.Bortoleto1, R.Magalhães-Paniago3 and M.A.Cotta1 Instituto de Física Gleb Wataghin, DFA/LPD, UNICAMP, CP 6165, 13081-970 Campinas-São Paulo, Brazil 2 Department of Physics, The Pennsylvania State University, 104 Davey Laboratory, University Park, PA 16802-6300, USA 3 Departamento de Física, UFMG, CP 702, CEP 30123-970, Belo Horizonte, Minas Gerais, Brazil 1
ABSTRACT In this letter we present results on the growth of InAs nanowires (NW’s) on InGaAs lattice-matched to (100) InP substrates by Chemical Beam Epitaxy. We observed that the nanostructure stability depends on the thickness of the InGaAs layer. This effect may result from two different conditions: the nanostructure strain field depth and/or compositional modulation in the buffer layer. Our investigation shows that anisotropic strain relaxation for nanowires grown on InGaAs is faster than for those grown on InP but the elastic energy in the nanostructures is no different from the InAs/InP case. These results suggest that the InAs strain relaxation does not depend significantly on the InGaAs buffer layer thickness. Nevertheless, transmission electron microscopy images show an additional stress field superimposed on that usually observed for the InAs nanostructures, which is attributed to compositional modulation in the ternary layer.
INTRODUCTION InAs nanostructures in an InGaAs/InP matrix (mismatch ~ 0.15%) have received much attention in the last years for the purpose of band gap engineering in quantum dot devices. Their potential application in light-emitting devices in the 1.3 – 1.5 µm wavelength range makes it necessary to understand and control the formation of these structures1-3. Recent results suggest that nanostructure stability2 and/or the chemical composition4 of the buffer layer (InP, InAlAs, or InGaAs) are determinant in configuring the final shape of the InAs nanostructures. Nevertheless, the conditions and mechanisms that originate each kind of nanostructure are not clear. In this letter we present results on the growth of InAs nanowires (NW’s) on InGaAs lattice-matched to (100) InP, and the influence of the InGaAs layers on the size and spatial distribution of the InAs NW’s. We observe the transition from wire to wire and dot and/or only dots on the surface depending on growth parameters. The influence of temperature, growth rate and InGaAs thickness on the NW’s formation was analyzed. Our results suggest that the periodic stress field from InGaAs layer modulation disrupts the formation of InAs NW’s.
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EXPERIMENTAL DETAILS The samples were grown by Chemical Beam Epitaxy (CBE) using trimethylindium (TMI) and triethylgallium (TEG) diluted with H2 carrier gas as the group III source and thermally decomposed phosphine (PH3) and arsine (AsH3) as group-V sources. The InP substrate native oxide was removed by heating the substrate during 10 minutes at 535oC in the growth chamber under P2 overpressure. Before I
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