Characterization of as‐grown and adsorbate‐covered N‐polar InN surfaces using in situ photoelectron spectroscopy

Abstract

The surface electronic properties and adsorption behaviour of as‐grown and oxidized N‐polar InN films are characterized by photoelectron spectroscopy (XPS, UPS). The epitaxial growth of the InN layers was performed by plasma‐assisted molecular beam epitaxy on GaN/6H‐SiC(000‐1). After growth and in situ characterization the InN surfaces were exposed to molecular oxygen to evaluate the adsorption behaviour of O2 on N‐polar InN and to study its impact on the surface electronic properties of the III‐nitride material. The results are compared with studies on In‐polar InN on GaN/sapphire templates. The as‐grown N‐polar InN surface exhibits a pronounced surface state at a binding energy of ∼1.6 eV. The valence band minimum lies about 0.8–1.0 eV below the surface Fermi level. Additionally, the XPS core level binding energies for InN(000‐1) are reduced compared to InN(0001) films, indicating different surface band bending for clean N‐polar and In‐polar InN, respectively. The interaction of molecular oxygen with the InN(000‐1) surface leads to a downward band bending by 0.1 eV compared to the initial state. Additional adsorption of species from the residual gas of the UHV chamber increases the surface downward band bending. Furthermore two pronounced oxygen related states with an energy distance of ∼5 eV could be detected in the valence band region. The adsorbed oxygen results in an additional component in the N1s core level spectra, which is interpreted as formation of NOx bonds.

Synchrotron radiation photoemission study of the ultrathin Cs/InN interface

“…The similar result was obtained for the InN surface using photon excitation energy of 90 eV [24]. In addition to that XPS studies reveal the valence band photoemission with two clearly defined maxima [11,12,[16][17][18][19][20][21][22][23][24][25]. The difference between UPS and XPS spectra can be related to the significant contribution in UPS results of both the surface and near surface regions.…”

“…The difference between UPS and XPS spectra can be related to the significant contribution in UPS results of both the surface and near surface regions. The shape and the bandwidth of the valence band spectrum coincide well with ones that are obtained previously by UPS [16][17][18][19][20][21][22][23][24]. The unresolved In 4d peak (spin-orbit split In 4d 3/2 and In 4d 5/2) is observed at binding energy of 15.1 eV with respect to E VBM .…”

“…The valence band spectra of wurtzite InN samples were studied by XPS and UPS [11,12,[15][16][17][18][19][20][21][22][23][24][25]. The XPS valence band spectrum consists usually of a broad band with two maxima at 1-3 eV and at 5-6 eV below the E VBM .…”

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

“…8,[19][20][21][22][23][24][25][26][27][28][29][30] For example, in general, the currently reported nominally undoped InN is n-type degenerate, with the residual electron densities in the range of ∼ 1 × 10 18 cm −3 , or higher. 8,11,25,[31][32][33][34] Moreover, it has been generally observed that there exists a very high electron concentration (∼ 1 × 10 13−14 cm −2 ) at both the polar and nonpolar grown surfaces of InN films, 19,35 and the Fermi-level (E F ) is pinned deep into the conduction band at the surfaces; 19,20,29,30 similar electron accumulation profile has also been measured at the lateral nonpolar grown surfaces of [0001]-oriented wurtzite InN nanowires. 8,11,21,22,25,36 In this regard, significant efforts have been devoted to understanding the fundamental surface charge properties of InN.…”

“…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.…”