Changes in the valence band structure of as‐grown InN(0001)‐2 × 2 surfaces upon exposure to oxygen and water

Abstract

We investigated the surface chemistry and valence band (VB) structure of as-grown thin InN(0001)-2 Â 2 films as well as their change upon the exposure to oxygen and water. The InN films were grown by plasma-assisted molecular beam epitaxy (PAMBE) and in situ characterized by reflection high electron energy diffraction (RHEED) and photoelectron spectroscopy (UPS, XPS). The oxygen and water exposure was directly performed on the as-grown, contamination-free InN surfaces at room temperature and leads to changes in the chemical surface states as well as the electronic properties. For 2 Â 2 reconstructed InN surfaces one observes directly after growth a surface state at the Fermi-edge which decreases continuously with oxygen and water exposure. Furthermore, two oxygen related electronic states develop in the VB at binding energies at around 5 and 10 eV. For water exposure a third weak state around 8 eV is additionally observed. The impact of oxygen and water on the work function F as well as the variation of surface band bending was investigated. In both cases for initially 2 Â 2 reconstructed surfaces a reduction in the downward band bending is found, while F increases in the case of oxygen exposure but in the case of interaction with water a reduced work function is observed. The oxygen uptake rates reveal a higher reactivity of water with InN surfaces compared to oxygen. Furthermore, during oxidation and water exposure different chemical oxygen bonds are formed, but a direct assignment to In-O or N-O bonds is difficult due to changes in the In3d and N1s XPS core level peak shape.

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

“…Therefore, we assign them to the occupied surface states which are related to the 2 Â 2 reconstruction. 4,22 According to the DFT results, the surface states determine the position of the surface Fermi level 0.7 eV above the CBM, which is in line with the band diagram shown in Fig. 2, and hence induce electron accumulation and downward bending at the InN(0001)-2 Â 2 surface.…”

“…All these surface states show a high reactivity during adsorbate exposure. 13,22 Note that for all InN surfaces an emission up to E F (partially connected with a slight increase in intensity at E F ) is measured due to the degenerated character of InN and the existence of occupied bulk states in the CB. A theoretical description of surface states and reconstructions at InN surfaces is already given by DFT studies of Segev and Van de Walle.…”

“…21 All these mechanisms seem to be connected with the presence of characteristic occupied and unoccupied surface states that determine the surface Fermi level position and thereby the surface electron accumulation. [5][6][7] Surface states were already experimentally observed for In-polar and Npolar InN films, 4,13,22 while no measurements for nonpolar InN exist.…”

Impact of potassium and water on the electronic properties of InN(0001) surfaces

“…For the implementation of InN in sensors and other devices, the control and modification of the surface electron density is a crucial point and demand a detailed understanding of the influence of adsorbates on the surface accumulation layer and electronic properties of InN. Previous experiments performing ozone-induced oxidation of InN(0001) films [14,15], anodic oxidation [16] as well as in-situ oxidation [17] have shown a depletion in electron concentration and also adsorbates containing strong electronegative sulfur induce a comparable effect [18]. Earlier studies also reported on modifications of the electronic and optical properties of polycrystalline InN in aqueous eletrochemical reactions [19,20] and via water electrolysis [21].…”

Interaction of indium oxide nanoparticle film surfaces with ozone, oxygen and water

“…For all performed experiments, a comparable change in the O1s spectrum as already discussed for ozone interaction was found and two significant spectral features in the valence band appear with an energy separation of 5.1 eV but slight deviations in absolute energy of 0.2 eV. Despite a slight change in absolute energy, these two structures are similar to the observed oxygen-induced adsorbate states in the VB spectra of In-polar and N-polar indium nitride (InN) after interaction with molecular oxygen or water having a comparable energy splitting [26][27][28]. Therefore, we assume the formation of the same adsorbate species in both cases.…”