The Electronic Energy Band Structure And Optical Properties Of Wurtzite Semiconductor:the First Principle Calculations

For electronic energy band structure and optical properties of the wurtzite InN and graphene are studied. And unique physical properties for doped InN and graphene are investigated detaily. Firstly, the phonon spectra and optical properties of wurtzite InN in the reststrahlen region are studied by the first-principle calculations based on the density functional theory. Secondly, the band gap of wurtzite InN is corrected using GGA+U in density functional theory. Furthermore, the electronic band structures, density of states (DOS) and projected density of states (PDOS) of the wurtzite In1-xGaxN are studied. The calculations of phonon spectra are based on the Generalized-Gradient Approximation (GGA). Finally, the charge density, electronic energy band and density of states of bare, H terminated and Li doped armchair graphene nanoribbons (AGNRs) are investigated using the local density approximation based on density function theory.The calculation indicates that InN has metal-like behavior. Also, Our calculation shows the reflectivity R at ω close to ωLO is nearly zero and R-1at ωTO<ω<ωLO.In the dispersion curves, there are a strong absorption peak of k(ω) at the resonance frequency ω=ωTO.These results show the fundamental vibration has dipole moment and is therefore infrared active in wurtzite structure semiconductors.Secondly, our calculations suggest that in the case of wurtzite InN it is important to apply GGA+U(p+d) in order to recover the correct bang gap and obtain a reliable description of InN band structure. The methodology is applied to study the electronic properties of the wurtzite In1-xGaxN. The increases in the band-gap and valence band width show that an anti-Stokes shift occurs with the band-gap variations due to the composition fluctuations. It was confirmed that the increases of the band gap and the valence-band width stem from the repulsion of p-d electrons and strong hybridizations during of the Ga-4,s, In-5s and Ga-4p, In-5p electrons.Finally, the bare AGNRs are an indirect band gap semiconductor. And the upper valence-band and conduction band are mainly dominated by C-2p states for the bare AGNRs. The H terminated AGNRs is direct band gap semiconductor with band gap1.68eV. The Fermi level crosses the conduction band and the ribbon becomes metallic for Li doped AGNRs. The one-edge Li-doped AGNRs have the lowest formation energy for other different doping configurations. So we can predict that one-edge Li-doped AGNRs is an energetically favorable practice for different doping configurations. The project density of states is calculated and reveals that the localization and hybridization between C-2p and Li-2p electronic states are much stronger in the conduction band group.