Photo-induced selective etching of GaN nanowires in water.

Nanowire (NW) based devices for solar driven artificial photosynthesis have gained increasing interest in recent years due to the intrinsically high surface to volume ratio and the excellent achievable crystal qualities. However, catalytically active surfaces often suffer from insufficient stability under operational conditions. To gain a fundamental understanding of the underlying processes, the photochemical etching behavior of hexagonal and round GaN NWs in deionized water under illumination are investigated. We find that the crystallographic c-plane remains stable, whereas the m-planes are photochemically etched with rates up to 11 nm min-1, depending on the applied UV light intensity. By investigating nanowalls, we achieve control of the exposed crystallographic facets and find an enhanced stability of the a-plane compared to the m-plane. Photo-excited holes, which drift to the side facets due to the upward surface band bending in nominally n-type (not intentionally doped) GaN, are identified as the driving force of the process, which allows the development of concepts for the stabilization of the nanostructures. A geometrically enhanced absorption of periodic NW arrays is correlated with a dependence of the etch rate on the NW pitch and diameter. Further, we find selective photochemical etching of the NW base in the presence of sub-band gap illumination, which is attributed to defect-related absorption in this region. These results provide improved understanding of the roles of inhomogeneous defect distribution, light excitation profiles, and different surface facets on the photochemical stability of nanostructures and provide viable strategies for improving stabilities under light-driven reaction conditions.

[1]  M. Stutzmann,et al.  Selectively grown GaN nanowalls and nanogrids for photocatalysis: growth and optical properties. , 2019, Nanoscale.

[2]  K. Bertness,et al.  Selective Area Growth and Structural Characterization of GaN Nanostructures on Si(111) Substrates , 2018, Crystals.

[3]  M. Stutzmann,et al.  A systematic investigation of radiative recombination in GaN nanowires: The influence of nanowire geometry and environmental conditions , 2018, Journal of Applied Physics.

[4]  M. Stutzmann,et al.  Optical design of GaN nanowire arrays for photocatalytic applications , 2018, Journal of Applied Physics.

[5]  M. Eickhoff,et al.  Photoelectrochemical response of GaN, InGaN, and GaNP nanowire ensembles , 2018 .

[6]  A. J. Frank,et al.  Passivation layers for nanostructured photoanodes: ultra-thin oxides on InGaN nanowires , 2018 .

[7]  Polarity Control of Heteroepitaxial GaN Nanowires on Diamond. , 2017, Nano letters.

[8]  M. Ramsteiner,et al.  p-Type Doping of GaN Nanowires Characterized by Photoelectrochemical Measurements. , 2017, Nano letters.

[9]  M. R. Wagner,et al.  Polarity in GaN and ZnO: Theory, measurement, growth, and devices , 2016 .

[10]  M. Stutzmann,et al.  Strain-Induced Band Gap Engineering in Selectively Grown GaN-(Al,Ga)N Core-Shell Nanowire Heterostructures. , 2016, Nano letters.

[11]  E. Calleja,et al.  Improving optical performance of GaN nanowires grown by selective area growth homoepitaxy: Influence of substrate and nanowire dimensions , 2016 .

[12]  M. Stutzmann,et al.  GaN nanowires on diamond , 2016 .

[13]  B. Haas,et al.  Attribution of the 3.45 eV GaN nanowires luminescence to inversion domain boundaries , 2015 .

[14]  A. Rizzi,et al.  Optical Emission of Individual GaN Nanocolumns Analyzed with High Spatial Resolution. , 2015, Nano letters.

[15]  Katsumi Kishino,et al.  Selective-area growth of GaN nanocolumns on Si(111) substrates for application to nanocolumn emitters with systematic analysis of dislocation filtering effect of nanocolumns , 2015, Nanotechnology.

[16]  M. Stutzmann,et al.  Kinetics of optically excited charge carriers at the GaN surface , 2015 .

[17]  M. Stutzmann,et al.  Position-controlled growth of GaN nanowires and nanotubes on diamond by molecular beam epitaxy. , 2015, Nano letters.

[18]  M. Stutzmann,et al.  Doped GaN nanowires on diamond: Structural properties and charge carrier distribution , 2015 .

[19]  C. Battaglia,et al.  Role of TiO2 Surface Passivation on Improving the Performance of p-InP Photocathodes , 2015 .

[20]  Enrique Calleja,et al.  Formation mechanisms of GaN nanowires grown by selective area growth homoepitaxy. , 2015, Nano letters.

[21]  Matthew R. Shaner,et al.  Amorphous TiO2 coatings stabilize Si, GaAs, and GaP photoanodes for efficient water oxidation , 2014, Science.

[22]  Z. Mi,et al.  Tuning the surface Fermi level on p-type gallium nitride nanowires for efficient overall water splitting , 2014, Nature Communications.

[23]  M. Stutzmann,et al.  p-GaN/n-ZnO heterojunction nanowires: optoelectronic properties and the role of interface polarity. , 2014, ACS nano.

[24]  J. Klein-Wiele,et al.  Corrigendum: Ga-polar GaN nanocolumn arrays with semipolar faceted tips (2013 New J. Phys. 15 053045) , 2014 .

[25]  A. Alivisatos,et al.  Luminescence studies of individual quantum dot photocatalysts. , 2013, Journal of the American Chemical Society.

[26]  Z. Mi,et al.  One-step overall water splitting under visible light using multiband InGaN/GaN nanowire heterostructures. , 2013, ACS nano.

[27]  K. Sabelfeld,et al.  Self-regulated radius of spontaneously formed GaN nanowires in molecular beam epitaxy. , 2013, Nano letters.

[28]  M. Stutzmann,et al.  Photocatalytic Cleavage of Self‐Assembled Organic Monolayers by UV‐Induced Charge Transfer from GaN Substrates , 2010, Advanced materials.

[29]  Hiroto Sekiguchi,et al.  Improved Ti-mask selective-area growth (SAG) by rf-plasma-assisted molecular beam epitaxy demonstrating extremely uniform GaN nanocolumn arrays , 2009 .

[30]  S. Denbaars,et al.  Smooth Top-Down Photoelectrochemical Etching of m-Plane GaN , 2009 .

[31]  D. Klug,et al.  Mechanism of photocatalytic water splitting in TiO2. Reaction of water with photoholes, importance of charge carrier dynamics, and evidence for four-hole chemistry. , 2008, Journal of the American Chemical Society.

[32]  Young Joon Hong,et al.  Photocatalysis using GaN nanowires. , 2008, ACS nano.

[33]  P. Vogl,et al.  nextnano: General Purpose 3-D Simulations , 2007, IEEE Transactions on Electron Devices.

[34]  Chris G. Van de Walle,et al.  Microscopic origins of surface states on nitride surfaces , 2007 .

[35]  Kazuhiro Ohkawa,et al.  Hydrogen Gas Generation by Splitting Aqueous Water Using n-Type GaN Photoelectrode with Anodic Oxidation , 2005 .

[36]  Thomas Richter,et al.  Size-dependent photoconductivity in MBE-grown GaN-nanowires. , 2005, Nano letters.

[37]  H. Morkoç,et al.  Luminescence properties of defects in GaN , 2005 .

[38]  P. Larsen,et al.  An electrochemical study of photoetching of heteroepitaxial GaN: kinetics and morphology , 2005 .

[39]  Charles M. Lieber,et al.  Synthesis of p-Type Gallium Nitride Nanowires for Electronic and Photonic Nanodevices , 2003 .

[40]  J. Weyher,et al.  Selective photoetching and transmission electron microscopy studies of defects in heteroepitaxial GaN , 2001 .

[41]  S. Moisa,et al.  Ultraviolet photoenhanced wet etching of GaN in K2S2O8 solution , 2001 .

[42]  H. Morkoç,et al.  Bias-assisted photoelectrochemical etching of p-GaN at 300 K , 2000 .

[43]  W. Gomes,et al.  Electrochemistry and Photoetching of n‐GaN , 2000 .

[44]  Pierre Gibart,et al.  TEMPERATURE QUENCHING OF PHOTOLUMINESCENCE INTENSITIES IN UNDOPED AND DOPED GAN , 1999 .

[45]  Ilesanmi Adesida,et al.  Rapid evaluation of dislocation densities in n-type GaN films using photoenhanced wet etching , 1999 .

[46]  C. Y. Chen,et al.  Deep ultraviolet enhanced wet chemical etching of gallium nitride , 1998 .

[47]  Ilesanmi Adesida,et al.  Dopant-selective photoenhanced wet etching of GaN , 1998 .

[48]  S. Haffouz,et al.  Luminescence and reflectivity studies of undoped, n- and p-doped GaN on (0001) sapphire , 1997 .

[49]  E. Hu,et al.  Room‐temperature photoenhanced wet etching of GaN , 1996 .

[50]  T. Matsumoto,et al.  Temperature Dependence of Photoluminescence from GaN , 1974 .