| dc.description.abstract | InN is an important compound in group-III nitride semiconductors and has attracted much attention due to its debated narrow energy gap (0.7-0.9eV). Recently, Hu et al. proposed a single crystalline InN nanobelts, and then Dong et. al. observed the X-ray absorption (XAS) and the X-ray emission (XES) spectra of InN thin film and nanobelt.
We first employed the first-principles calculation, i.e. Quantum Espresso, with the local-density approximation (LDA) to study the structural properties of InN bulk, thin film in wurtzite (0001) direction, and nanobelt enclosed by wurtzite ±(0001) and ±(11 ̅00) planes. For the InN thin film, the saturation effect of H-saturated, O-saturated, and bare surface on the polar (0001) plane are considered. The subtle surface charge transfer, due to the different electronegativities between ions, gives rise to the opposite In- and N-terminated surface geometry between H- and O-saturated thin films. Moreover, our DFT+LDA calculation suggests that the critical thickness of bare InN polar thin film is 6-bilayer, since we observed the structural transfer from the wurtzite structure with sp3 bond geometry in 6-bilayer case into the graphitic structure with sp2 bond geometry in 4-bilayer case. Interesting, for the H-saturated InN nanobelt, we observe the tilted interfacial In-N bonds, due to the smaller (larger) electronegativity between In (N) and H ions.
In order to resolve the underestimate of energy gaps of N-based semiconductors, the newly proposed matrix method for the nonlocal exchange potential with the pseudofunction (PSFEXX) method is employed and then gives excellent agreement between calculated 0.7eV (6.0eV) and experimental 0.7-0.8eV (6.2eV). We strongly believe that this PSFEXX method may provide more reliable structural and electronic properties in low-dimensional InN materials, where those misleading surface states near the zero or negative energy gap of InN by LDA or GGA calculation can be efficiently corrected and then play a significant role on the structural properties. | en_US |