| 1. |
- Ahuja, Rajeev, et al.
(author)
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Electronic and optical properties of lead iodide
- 2002
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In: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 92:12, s. 7219-7224
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Journal article (peer-reviewed)abstract
- The electronic properties and the optical absorption of lead iodide (PbI2) have been investigated experimentally by means of optical absorption and spectroscopic ellipsometry, and theoretically by a full-potential linear muffin-tin-orbital method. PbI2 has been recognized as a very promising detector material with a large technological applicability. Its band-gap energy as a function of temperature has also been measured by optical absorption. The temperature dependence has been fitted by two different relations, and a discussion of these fittings is given.
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| 2. |
- Ahuja, Rajeev, et al.
(author)
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Optical properties of 4H-SiC
- 2002
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In: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 91:4, s. 2099-2103
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Journal article (peer-reviewed)abstract
- The optical band gap energy and the dielectric functions of n-type 4H-SiC have been investigated experimentally by transmission spectroscopy and spectroscopic ellipsometry and theoretically by an ab initio full-potential linear muffin-tin-orbital method. We present the real and imaginary parts of the dielectric functions, resolved into the transverse and longitudinal photon moment a, and we show that the anisotropy is small in 4H-SiC. The measurements and the calculations fall closely together in a wide range of energies.
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| 3. |
- Ahuja, Rajeev, et al.
(author)
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Optical properties of SiGe alloys
- 2003
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In: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 93:7, s. 3832-3836
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Journal article (peer-reviewed)abstract
- The optical properties of Si1-xGex have been investigated theoretically using a full-potential linear muffin-tin-orbital method. We present the density-of-states as well as the real and imaginary parts of the dielectric function. The calculated dielectric function was found to be in good agreement with the spectroscopic ellipsometry measurements by J. Bahng , J. Phys.: Condens. Matter 13, 777 (2001), and we obtained a static dielectric constant of epsilon(0)=12.19+2.45x in the Si rich regime (xless than or equal to0.5).
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| 4. |
- da Silva, A. F., et al.
(author)
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Influence of Si doping on optical properties of wurtzite GaN
- 2001
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In: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 13:40, s. 8891-8899
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Journal article (peer-reviewed)abstract
- The band gap shift (BGS) of Si-doped wurtzite GaN for impurity concentrations spanning the insulating to the metallic regimes has been investigated at low temperature. The critical impurity concentration for the metal-non-metal transition is estimated from the generalized Drude approach for the resistivity to be about 1.0 x 10(18) cm(-3). The calculations for the BGS were carried out within a framework of the random phase approximation, taking into account the electron-electron, electron-optical phonon, and electron-ion interactions. In the wake of very recent photoluminescence measurements, we have shown and discussed the possible transitions involved in the experimental results.
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| 5. |
- da Silva, A. F., et al.
(author)
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Optical properties of oxide compounds PbO, SnO2 and TiO2
- 2004
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In: Physica Scripta. - 0031-8949 .- 1402-4896. ; T109, s. 180-183
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Journal article (peer-reviewed)abstract
- The optical properties of the oxide compounds PbO and SnO2 have been investigated experimentally by transmission spectroscopy measurements and theoretically by a full-potential linearized augmented plane wave (FPLAPW) method. The dielectric functions of the rutile TiO2 has also been calculated. The calculated band-gap energies as well as the optical absorption were found to be in a very good qualitatively agreement with the experimental results.
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| 6. |
- Persson, Clas, et al.
(author)
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Effective electron and hole masses in intrinsic and heavily n-type doped GaN and AlN
- 2001
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In: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 13:40, s. 8915-8922
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Journal article (peer-reviewed)abstract
- We have investigated the electronic structure near the band edges in intrinsic and heavily n-type doped GaN and AlN. Both the wurtzite and the zincblende polytypes have been considered. The electronic structures of the intrinsic materials were obtained from a full-potential linearized augmented plane wave calculation. We show the importance of performing a fully relativistic calculation. For instance, the hole mass in cubic AIN is a very large and negative quantity if spin-orbit coupling is excluded, whereas the fully relativistic calculation gives a relatively small and positive value. The electron-phonon coupling was taken into account according to the Frohlich Hamiltonian for large polarons, resulting in effective polaron masses. The effects on the effective electron masses due to doping were investigated by using a Green's function formalism within the random phase approximation and with a local-field correction according to Hubbard.
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| 7. |
- Persson, Clas, et al.
(author)
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Effective electronic masses in wurtzite and zinc-blende GaN and AlN
- 2001
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In: Journal of Crystal Growth. - 0022-0248 .- 1873-5002. ; 231:3, s. 397-406
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Journal article (peer-reviewed)abstract
- The effective electron and hole masses are fundamental quantities of semiconductors, used in numerous analyses of experiments and theoretical investigations. We present calculations of the band structure near the band edges in intrinsic GaN and AIN, both for the wurtzite and the zinc-blende polytypes. We have utilized a full-potential linearized augmented plane wave method within the density functional theory and with two different exchange-correlation potentials. The lattice parameters have been determined by a minimization of the total energy, whereupon the crystal-field splitting, the spin-orbit splitting, and the effective electron and hole masses have been calculated. The calculated effective masses are in good agreement with available experimental values. We show the importance of performing a fully relativistic calculation. For instance, the hole mass in cubic AIN is a very large and negative quantity if the spin-orbit coupling is excluded, whereas the fully relativistic calculation gives a relatively small and positive value.
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| 8. |
- Persson, Clas, et al.
(author)
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First-principle calculations of optical properties of wurtzite AlN and GaN
- 2001
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In: Journal of Crystal Growth. - 0022-0248 .- 1873-5002. ; 231:3, s. 407-414
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Journal article (peer-reviewed)abstract
- The imaginary part of the dielectric function of wurtzite AIN and GaN has been calculated in the long wavelength limit, using two different first-principle electronic structure methods. The first method is a full-potential linearized augmented plane wave method and the second is a full-potential linear muffin-tin orbital method. From the Kramers-Kronig dispersion relations the real part of the dielectric function has been obtained, taking into account a quasi-particle band-gap correction according to Bechstedt and Del Sole. Absorption due to optical phonons is treated as a delta function in the imaginary part of the dielectric function. Both the longitudinal as well as the transverse components of the dielectric function are presented, showing that the anisotropy is small in these materials. Although we use different correlation potentials in the two methods, the results are similar, We compare our calculated dielectric functions with spectroscopic ellipsometry and reflectance spectra measurements.
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| 9. |
- Persson, Clas, et al.
(author)
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First-principle calculations of the dielectric function of zinc-blende and wurtzite InN
- 2001
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In: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 13:40, s. 8945-8950
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Journal article (peer-reviewed)abstract
- The imaginary part of the dielectric function of zinc-blende and wurtzite InN has been calculated using a full-potential linearized augmented plane wave method. We show that the exchange potential of Engel and Vosko gives an insulating ground state for both structures. The real part of the dielectric function has been obtained from the Kramers-Kronig dispersion relations, assuming a quasiparticle band-gap correction according to Bechstedt and Del Sole. We have found that it is necessary to have a good account of the band gap in order to derive the low-frequency optical properties. We present the longitudinal as wen as the transverse components in wurtzite InN, showing that the anisotropy is small.
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| 10. |
- Persson, Clas, et al.
(author)
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Metal-nonmetal transition in p-type SiC polytypes
- 2001
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In: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 6320:20
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Journal article (peer-reviewed)abstract
- The critical concentration for the metal-nonmetal transition has been calculated fur the polytypes 3C, 4H, and 6H of SiC, duped with Al, Ga, B, and Sc. Three different computational methods have been utilized: the first is Mott's original model, the second is an extended Mott-Hubbard model, and the third is based on the total energy of the metallic and nonmetallic phases. All three methods show similar results. For comparison, calculations fur p-type Ge and Si materials have also been performed.
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