Direct measurement of the band gap and Fermi level position at InN(112¯)

Abstract

A nonpolar stoichiometric InN(112¯0) surface freshly cleaved inside UHV was investigated by scanning tunneling microscopy and spectroscopy. Due to the absence of intrinsic surface states in the band gap, scanning tunneling spectroscopy yields directly the fundamental bulk band gap of 0.7±0.1 eV. The Fermi energy is pinned 0.3 eV below the conduction band minimum due to cleavage induced defect states. Thus, intrinsic electron accumulation can be excluded for this surface. Electron accumulation is rather an extrinsic effect due to surface contamination or material decomposition, but not an intrinsic material property of InN.

Surface states and electronic structure of polar and nonpolar InN – An in situ photoelectron spectroscopy study

“…While DFT calculations predict a reduction or even the absence of surface downward band bending, 5-7 experimental results showed a strong electron accumulation. [8][9][10] Only recently, the theoretical predictions were supported by measurements at cleaved a-plane, 11,12 as-grown N-polar, 13 as well as chemically treated a-plane, m-plane, and N-polar InN surfaces. [14][15][16][17] So far, the experimental results together with theoretical conclusions indicate that the occurrence of electron accumulation at InN surfaces strongly depends on surface reconstructions, 4,18 the formation of In-adlayers, [18][19][20] as well as adsorbates 13,20 or dopants.…”

“…Here, we present the in situ characterization of the electronic structure of stoichiometric InN(0001)-2 Â 2, InN(000-1), InN(1-100), and InN (11)(12)(13)(14)(15)(16)(17)(18)(19)(20) surfaces by X-ray and ultraviolet photoelectron spectroscopy (XPS, UPS). Depending on the crystal orientation, different occupied surface states are identified and differentiated from contributions of the bulk band structure by comparison with available DFT studies.…”

Understanding the role of Si doping on surface charge and optical properties: Photoluminescence study of intrinsic and Si-doped InN nanowires

“…In terms of nonpolar InN surface, recent studies suggest that the surface electron accumulation may depend critically on the surface states, impurities, stoichiometry, and polarity; 27,37 and the absence of electron accumulation at nonpolar surface has been predicted. 23,27 In experiments, however, only recent cross-sectional scanning photoelectron microscopy and spectroscopy studies at nonpolar cleaved InN surface exhibits the unpinned E F , 38,39 while in general the electron accumulation is prevalently observed at nonpolar InN surface; 22,34,35 the electron accumulation issue at nonpolar InN surface had remained elusive.…”

“…8,11,21,22,25,36 In this regard, significant efforts have been devoted to understanding the fundamental surface charge properties of InN. 20,23,27,29,30,[37][38][39] The electron accumulation at polar InN surface has been explained by the presence of large density of the occupied In-In bond states above the conduction band minimum (CBM), 23 as well as the unusual positioning of the branch point energy (E B ) well above the CBM at the Γ-point, which allows donor-type surface states to exist in the conduction band; 20 for polar InN surface, theoretical studies agree well with experiments. In terms of nonpolar InN surface, recent studies suggest that the surface electron accumulation may depend critically on the surface states, impurities, stoichiometry, and polarity; 27,37 and the absence of electron accumulation at nonpolar surface has been predicted.…”

Effect of catalyst nanoparticle size on growth direction and morphology of InN nanowires

“…9 Sometimes, it happens that both the VLS and VS processes concurrently take place in one crystal growth process. 9,10 InN, as an important III-V compound semiconductor with a direct band gap energy of about 0.7 eV at room temperature 11 and surface electron accumulation, 12 has attracted growing attention owing to its good performances in semiconductor optoelectronic, 13 Tera-Hertz emission devices, 14,15 as well as high-speed heterojunction FETs. 16 At present, plentiful InN nanostructures, including NWs, 3 nanorods, 17 nanotubes, 18 nanobelts, 19 nanonetworks 20 and nanoflowers 21 have been reported.…”