The electronic structures of potassium doped ZnO have been calculated by first principles plane wave-function psuedopotential approach based on density-functional theory and local density approximation. Properties of some defects were studied in order to explicate the conductivity mechanism of p-K:ZnO, including hydrogen interstitial (Hi), oxygen vacancy (VO), zinc interstitial (Zni) and zinc vacancy (VZn). The calculated results revealed that: (1) K-doping introduced a shallow acceptor,besides increasing the system total energy simultaneously. (2) K-H:ZnO decreased the system energy and increased the system stability. (3) Although the formation of VO was more difficult than that of Zni, both of them were electronegative centers and played a role in compensating for the acceptors. (4) VZn produceda shallow acceptor approximately 0.5 eV above the maximum valence band, which was beneficial for p-type conductivity. Finally, it was proposed that the realization of p-type conductivity in K:ZnO may be due to the formation of a KZn-O-Hi-O-VZn complex.

The Raman scattering spectra of the nitrogen doped n-SiC is studied. The theoretical line shape analysis indicates that, compared with 4H-SiC, the shift of the LO phonon-plasma coupled mode in 6H-SiC with free carrier concentration is smaller. From the electronic Raman spectra, which were obtained with laser excitation at 5145nm, there are four spectral lines in 6H-SiC and two lines in 4H-SiC, which correspond to the 1s(A1) to 1s(E) valley orbit transitions at the inequivalent k site. The explanation of the high-frequency signals of 6303 and 635 cm-1 is that they are velated with transitions at active deep level of defect. Finally, the second-order Raman features of 6H- and 4H-SiC are identified using the selection rules for second-order scattering in wurtzite structure.

Micro-Raman scattering from the nitrogen doped n-SiC is performed at the temperatures ranging from 100 to 450 K. The temperature dependences of the first-order Raman scattering, electronic Raman spectra and the second-order Raman features are obtained. These measurements reveal that most of the first-order Raman phonon frequencies decrease with temperature increasing, but the redshifts of the acoustic phonon modes are smaller than those of the optical phonon modes. Meanwhile, the longitudinal optical phonon-plasma coupled (LOPC) mode manifests different features with temperature increasing. The LOPC mode tends to have a blueshift at a lower temperature but a redshift at a higher temperature. This indicates that the temperature dependence of LOPC mode is affected not only by the anharmonic effects, but also by the ionized donor concentration. With the increase of the measurement temperature, the intensity of the electronic Raman spectrum decreases, and the linewidth gradually broadens, but the electronic Raman signal is almost not shifted. The redshift of the second-order Raman spectrum is smaller than that of the first-order Raman spectrum, but the intensity of the second-order Raman spectrum substantially decreases with the increase of temperature.

The electronic structures of the intrinsic and nitrogen-doped silicon carbide nanotubes （SiCNTs） have been calculated by first-principles approach based on the density functional theory. The intrinsic （8, 0） SiCNT is a direct band-gap semiconductor with a gap value of 0.94 eV. The band-gap of the SiCNT with the doping concentration of nitrogen being 1.56% and 3.12％ is narrowed to 0.83 eV and 0.74 eV， respectively. The narrowing of the band-gap is the result of the weakening of the Si-N bonds compared with the corresponding Si-C bonds, which can be seen by comparing the charge density difference of the intrinsic SiCNT with that of the nitrogen-doped nanotube.

By using first principles calculation based on density functional theory, band structures, densities of states and electron density differences for an ideal (6, 0) ZnO nanotube (ZnONT), Al doped, N doped and Al, N co-doped nanotubes are investigated. The calculated results reveal that the doped nitrogen atom results in the formation of acceptor level in the band gap of the ZnONT, which indicates that the doped nanotube has the characteristic of a p-type semiconductor. While the high locality of the acceptor level leads to a lower solubility for the doped nitrogen atoms, the acceptor level is broadened and shows delocalizing characteristics in nanotube with Al, N co-doped. This co-doping may be an efficient method of preparing p-type ZnONTs.