title: Strain-Induced Band Gap Engineering in Selectively Grown GaN-(Al,Ga)N Core-Shell Nanowire Heterostructures.
abstract: We demonstrate the selective area growth of GaN-(Al,Ga)N core-shell nanowire heterostructures directly on Si(111). Photoluminescence spectroscopy on as-grown nanowires reveals a strong blueshift of the GaN band gap from 3.40 to 3.64 eV at room temperature. Raman measurements relate this shift to compressive strain within the GaN core. On the nanoscale, cathodoluminescence spectroscopy and scanning transmission electron microscopy prove the homogeneity of strain-related luminescence along the nanowire axis and the absence of significant fluctuations within the shell, respectively. A comparison of the experimental findings with numerical simulations indicates the absence of a significant defect-related strain relaxation for all investigated structures, with a maximum compressive strain of -3.4% for a shell thickness of 50 nm. The accurate control of the nanowire dimensions, namely, core diameter, shell thickness, and nanowire period, via selective area growth allows a specific manipulation of the resulting strain within individual nanowires on the same sample. This, in turn, enables a spatially resolved adjustment of the GaN band gap with an energy range of 240 meV in a one-step growth process.
authors: Walter Schottky Institut and Physics Department, Technische Universität München , 85748 Garching, Germany.
authors: Martin
authors: M
authors: Hetzl
authors: Walter Schottky Institut and Physics Department, Technische Universität München , 85748 Garching, Germany.
authors: Max
authors: M
authors: Kraut
authors: Walter Schottky Institut and Physics Department, Technische Universität München , 85748 Garching, Germany.
authors: Julia
authors: J
authors: Winnerl
authors: Laboratoire des Matériaux Semiconducteurs, École Polytechnique Fédérale de Lausanne , 1015 Lausanne, Switzerland.
authors: Luca
authors: L
authors: Francaviglia
authors: Department of Chemistry, Ludwig-Maximilians-Universität München , 81377 Munich, Germany.
authors: Markus
authors: M
authors: Döblinger
authors: Walter Schottky Institut and Physics Department, Technische Universität München , 85748 Garching, Germany.
authors: Sonja
authors: S
authors: Matich
authors: Laboratoire des Matériaux Semiconducteurs, École Polytechnique Fédérale de Lausanne , 1015 Lausanne, Switzerland.
authors: Anna
authors: A
authors: Fontcuberta I Morral
authors: Walter Schottky Institut and Physics Department, Technische Universität München , 85748 Garching, Germany.
authors: Martin
authors: M
authors: Stutzmann
keywords: Nanowires; Raman scattering; band gap engineering; cathodoluminescence; core−shell; heteroepitaxy; photoluminescence; selective area growth; strain