0000000000240404
AUTHOR
S. Gilliland
Electronic structure of CuAlO2 and CuScO2 delafossites under pressure
The electronic structure of CuAlO 2 and CuScO 2 delafossites is investigated by means of optical absorption measurements under pressure and ab initio band structure calculations. Measurements are carried out on CuAlO 2 monocrystals and pulsed laser deposited CuAlO 2 and CuScO 2 thin films up to 20 GPa. CuAlO 2 is an indirect semiconductor that is stable in the pressure range explored here. The pressure coefficients of the indirect and direct gaps are found to be 15 meV/GPa and 2 meV/GPa respectively. CuScO 2 is a direct semiconductor and the pressure coefficient of the excitonic peak energy is -5.5 meV/GPa. Two reversible phase transitions are observed in CuScO 2 . At 13 GPa the delafossite…
Pressure and temperature dependence of the band-gap in CdTe
In this paper we report on isothermal compression measurements (up to 5 GPa and 500 K) of the optical absorption edge of 1 μm epitaxial layers of CdTe growth by metalorganic chemical vapor deposition (MOCVD) on GaS substrates. The isothermal blue shift under pressure of the direct energy gap (Γ v 15 → Γ c 1 ) in the zinc-blende phase is about 7.1 × 10 -2 eV GPa -1 and is found to be independent of temperature within the experimental errors. The isobaric red shift in the stability range of the zinc-blende phase is about -3.76 × 10 -4 eV K -1 . Regarding the phase transitions, no discontinuity in the energy gap has been found in the narrow pressure range where the cinnabar phase can be presen…
Variation of the optical absorption edge in AgGaS2 single crystals at high pressure
In this paper the optical absorption edge of AgGaS 2 is measured as a function of pressure up to 26 GPa in order to verify the effect of the three phases transitions occurring in that pressure domain. The direct energy gap increases linearly with pressure at the rate of about 4.0 x 10 -2 eV GPa -1 up to 10.2 GPa. The absence of any discontinuity in the energy gap in the pressure range of 4.2-10.2 GPa confirms that the volume change, in the chalcopirite to monoclinic second-order transition, if it exists, is very small. When the pressure is raised above 10.2 GPa, the energy gap drops suddenly by about 1.1 eV and the spectral form of the absorption coefficient is typical of semiconductors wit…
Electronic structure of p-type ultraviolet-transparent conducting CuScO2 films
Abstract We investigate the electronic structure of CuScO 2 thin films grown on sapphire and mica substrates by pulsed laser deposition. X-ray diffraction and microanalysis confirm that the films have the expected delafossite crystal structure and stoichiometric proportions. The electronic structure is investigated by means of X-ray and ultraviolet photoelectron spectroscopy. Electronic states in the range 0–1350 eV are identified, making reference to theoretical density-of-states calculations up to 80 eV. Photoelectron spectra near the Fermi energy confirm the p-character of the films. Optical absorption spectroscopy shows that the films are transparent up to 3.7 eV and exhibit an intense …
High pressure and high magnetic field behaviour of free and donor-bound-exciton photoluminescence in InSe
We report here first magneto-photoluminescence investigations under high pressure up to 6 GPa on III-VI layered semiconductor InSe. Both diamagnetism and magnetic field induced gap opening driven by Landau quantization became observable by using a 60 T pulsed magnet. The pressure-induced enhancement of the diamagnetic coefficient is consistent with the increase of the dielectric constant under pressure while the evolution of the linear coefficient is consistent with a slight increase of the electron effective mass up to 4 GPa and a direct-to-indirect conduction-band crossover around that pressure.
Role ofp-dands-dinteractions in the electronic structure and band gap of Zn1−xMxO (M=Cr, Mn, Fe, Co, Ni, and Cu): Photoelectron and optical spectroscopy and first-principles band structure calculations
We report an investigation on the effect of $p$-$d$ and $s$-$d$ interactions in the electronic structure, and especially in the band-gap value, of wurtzite wide-gap diluted magnetic semiconductors Zn${}_{1\ensuremath{-}x}$${M}_{x}$O ($M=\mathrm{Cr}$, Mn, Fe, Co, Ni, Cu). Thin films prepared by pulsed laser deposition are investigated by means of optical absorption at low-temperature and photoelectron spectroscopy. Pure wurzite phase is shown to be maintained for Co and Mn concentrations up to 25$%$ and for Cr up to 10$%$, while in the case of Fe, Ni, and Cu, other phases are present for concentrations higher than 5, 2, and 1$%$, respectively. The band gap of the Zn${}_{1\ensuremath{-}x}$${M…
GaS and InSe equations of state from single crystal diffraction
We have performed single crystal angle dispersive X-ray diffraction at high pressure in order to investigate the GaS and InSe equations of state. We situate the transition from β-GaS to GaS-II at 2 7 0 3. ± . GPa. In the InSe experiment we locate the beginning of the phase transition at 7.6 ± 0.6 GPa. The equations of state of β-GaS ( 0 43 27 0 06V = . ± . Å 3 , 37 2 GPaB = ± , 5 2B = .¢ ), GaS-II ( 0 42 4 0 2V = . ± . Å 3 , 50 3 GPaB = ± and 4 3 0 3B = . ± .¢ ) and γ-InSe ( 0 58 4 0 2V = . ± . Å 3 , 24 3 GPaB = ± and 8 6 0 8B = . ± .¢ ) are discussed and compared with the results of an ab-initio calculation.
Electronic structure and optical properties of CdTe rock-salt high pressure phase
This paper reports on optical absorption and reflectance measurements in thin CdTe samples up to 15 GPa. All studied samples become virtually opaque at the pressure transition between the zinc-blende and rock-salt phases (3.9 GPa). As pressure increases up to 10 GPa, a relative transparency region is observed between 1.2 eV and 2.4 eV, whose high energy edge shifts to higher photon energies. Above 10 GPa the transparency region gradually shrinks and disappears at about 11 GPa. The low energy side of the absorption spectrum is attributed to free carrier absorption, as electronic structure calculations show that rock-salt CdTe is a semimetal or a low gap semiconductor. Band filling effects lo…
Bistable phase locking in rocked lasers
Abstract We investigate analytically and numerically the dynamics of single mode lasers with periodic ac injection (rocked lasers). Such lasers show phase bistability as the phase of the light emitted by such lasers can lock to either of two values shifted by π. Locking regimes for different lasers are studied showing that the system response is strongly modified in class B lasers due to the influence of relaxation oscillations.
Buildup and structure of theInSe∕Ptinterface studied by angle-resolved photoemission and x-ray absorption spectroscopy
The atomic structure and the electronic nature of the $\mathrm{In}\mathrm{Se}∕\mathrm{Pt}$ interface have been studied by x-ray absorption spectroscopy and angle-resolved photoemission, respectively. By these measurements, it has been found that Pt atoms equally incorporate into two trigonal-prismatic intralayer positions existing within the InSe layer, although, at low Pt coverage, Pt atoms seem to prefer one of these sites, where they have a lower interaction with Se atoms. The atomic structure of the $\mathrm{In}\mathrm{Se}∕\mathrm{Pt}$ interface appears to determine its electronic behavior as Pt deposition increases. At initial stages of Pt diffusion, isolated Pt atoms act as a surface …