Determination of the wurtzite content and orientation distribution of nanowire ensembles
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1206-M11-39
Determination of the wurtzite content and orientation distribution of nanowire ensembles Dominik Kriegner1, Mario Keplinger1, Julian Stangl1, Aaron M. Andrews2, Pavel Klang2, Bernhard Mandl1,3, Thomas Mårtensson3, Magnus Borgstrom3, Knut Deppert3, Lars Samuelson3 Gottfried Strasser2 and Günther Bauer1 1
Institute of Semiconductor and Solid State Physics, University Linz, Altenbergerstrasse 69, 4040 Linz, Austria 2 Institute of Solid State Electronics, Vienna University of Technology, Floragasse 7, 1040 Vienna, Austria 3 Solid State Physics, Lund University, Box 118, S-22100 Lund, Sweden ABSTRACT We present x-ray diffraction based methods to quantitatively determine the wurtzite content of nanowire ensembles and to investigate the effect of twinning. An increased lattice constant in growth direction is found for all investigated InAs and InP nanowire samples. This increase is independent of the wurtzite content. Using x-ray pole figures we find that twinning is present in GaAs/Si branched nanowires, which leads to 60° rotations of the lattice. INTRODUCTION Semiconductor nanowires (NW) are promising candidates for future large scale devices. To fabricate such devices a precise control of the structural properties is required. In III-V semiconductor NWs quite often stacking faults and twin-planes are observed [1,2]. Although for the investigated materials (InP, InAs) the zinc-blende (ZB) phase is the stable one in bulk materials, in NWs stacking faults quite often introduce wurtzite (WZ) segments [1-5]. This corresponds to a change of the stacking order in the [111] direction from ABCABC (ZB phase) to ABAB (WZ phase). It influences the electronic band structure [6], and thus control of structural properties is important for device performance. A powerful tool to analyze the crystal structure of NWs is x-ray diffraction (XRD), with which single wires [2,7] as well as large NW ensembles can be investigated [8,9], and it is sensitive to strain [10]. We use XRD to investigate NW ensembles with respect to their epitaxial relationship to the substrate and their orientation distribution. From the Bragg reflection strengths we quantitatively determine the WZ content in NW ensembles. For branched GaAs/Si wires on Si, we show another effect of altered stacking sequence along the [111] direction, namely twinning which is accessible from x-ray pole figures. EXPERIMENT In the study of the crystal structure we are considering different sample series with either InAs or InP wires on various substrates grown at Lund University. Wires are grown by metal organic vapor phase epitaxy (MOVPE). To initiate the wire growth different procedures are used for the different sample series. A growth time series (Tx) and growth temperature series (Cx) are InAs NWs on InP (111)B and Si (111) substrates and were grown with a gold catalyst-free process. A doping series (Dx) consists of InP NWs on InAs (111)B surfaces; these are grown using Au particles as catalysts for the NW growth. For the gold-free samples, prior to growth, the
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