Infrared Study of Lattice and Free Carrier Effects in p-Type CuGe2P3 (original) (raw)
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Infrared reflectivity study of (Cu2GeS3)1?x (CuGe2P3) x solid solutions
Journal of Materials Science Letters, 1990
Recently it has been established that the ternary compounds Cu2GeS3 and CuGezP3 form a continuous series of solid solutions over the whole composition range [1]. On the basis of X-ray powder diffraction studies of (Cu2GeS3)~_x(CuGe2P3)x solid solutions with compositions x = 0.2, 0.5 and 0.8 it has been argued that these alloys crystallize in the zinc blende structure with a random distribution of the copper and germanium atoms on the cation sites and of the sulphur and phosphorus atoms on the anion sites [l-3]. The zinc blende structure with a random distribution of the copper and germanium atoms on the cation sites has also been reported for CuGe2P3 by various researchers [4-6]. However, in the case of Cu2GeS 3 it follows from X-ray structure studies on single crystals [7] as well as from infrared lattice vibration investigations in the frequency range of both the fundamental lattice modes [8] and the two-phonon combination modes [9] that this compound crystallizes in a monoclinic lattice with an ordered distribution of the ,copper and germanium atoms on the cation sites. In principle it cannot be completely excluded that (Cu2GeS3)~_x(CuGe2P3)x alloys with small x values crystallize in a non-cubic lattice, too, since it is known from X-ray structure studies of Cu2GeS3 that the reflections characteristic of the monoclinic structure are very weak, indistinct or even absent in powder diffraction diagrams [10, l 1]. In view of this fact it is obvious that careful X-ray diffraction measurements o n (C u 2 Q e S 3) I x (C u G e z P 3) x
On the temperature dependence of the electrical and optical properties of CuGeSe
Journal of Applied …, 2000
The Hall effect and electrical resistivity measurements on p-type Cu 2 GeSe 3 crystals were measured in the temperature range from 80 to 300 K. The temperature variation of the hole concentration p from about 200 to 300 K is explained as due to the thermal activation of a shallow acceptor level with an ionization energy of around 50 meV. At low temperatures the impurity band conduction dominates the electrical transport processes. From the analysis of the p vs T data, the density-of-states hole effective mass is estimated to be of the same magnitude as the free electron mass. The temperature variation of the hole mobility in the valence band is analyzed by taking into account the scattering of charge carriers by ionized impurities and acoustic phonons. In the impurity band, the mobility is explained as due to thermally activated hopping transport. The optical absorption coefficient spectrum shows the presence of three absorption narrow bands below the fundamental gap. From the analysis of their temperature dependence, these bands are attributed as due to free-to-bound transitions related to intrinsic defect acceptor states. Activation energies of these states are estimated to be around 0.12, 0.24, and 0.30 eV. Tentative assignment of the nature and origin of these defect states were also made.
Solar Energy Materials and Solar Cells, 1992
The growth conditions, the composition and the structural, optical and electrical properties of thin films of CuGaSe 2 and CuGaTe 2 have been studied using "flash" and "slow" evaporation in vacuum. Single phase films, when analyzing the absorption coefficient, present several energy gaps. For CuGaSe> they are 1.59, 1.66, 2.03 and 2.11 eV, for CuGaTe 2 1.23 and 1.89 eV. Both the CuGaSe~ and CuGaTe 2 evaporated films are p-type; the resistivities, carrier densities and mobilities are appropriate for thin film solar cells.
Dependence of optical properties on structural and compositional parameters in CuGaSe2
Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 2000
The dielectric constant of CuGaSe2 as a function of stoichiometric deviations has been obtained from photomodulated spectral ellipsometry measurements. Optical gaps have been computed by fitting experimental and differentiated data of the imaginary part of the dielectric constant to function ε2 of the Lorentz model and to the second derivative of ε2. In each sample, three transition energy values have been found in the 1.65–1.72, 1.83–1.95, and 2.97–3.14 eV ranges. The presence of point defects reduces the energy gap values. For nonstoichiometric samples, changes in the first energy gap values have been analyzed as a function of the displacement of the position of the anion in the unit cell. The shifts in the valence band structure have been analyzed and it is concluded that the difference between the first and second transition energies, (Eg2−Eg1), is also affected by stoichiometric deviations, so that the Γ5v(2) level in samples with point defects is closer to Γ4v(2) level than in...
Surface gap and surface electronic states in CuGeO3 single crystal
Surface Science, 1999
The surface and bulk electronic excitations of CuGeO3 are investigated by means of electron energy loss and polarized X-ray absorption spectroscopy. CuGeO3 shows a surface charge transfer gap of about 3.0±0.3eV. The unoccupied oxygen derived density of states, as probed by X-ray absorption at the O 1s edge, is in good agreement with recent many-body calculations.
Optical Absorption Studies on p–CuGa0.25In0.75.Se2 Thin Films
Physica Status Solidi (a), 1991
Optical Absorption Studies on p-C u G a c , 251no 7 5 S e Z Thin F i l m s By Y. APARNA, P.S. REDDY, B. SRINIVASIJLU NAIDU, and P. JAYARAMA REDDY CuInSe2 and CuGaSe have proved to be stable and efficient absorber materials for thin film heterojunction solar cells /I to 5 /. These ternary chalcopyrite compounds are direct bandgap semiconductors showing a threefold optical structure I6 / near the fundamental edge due to crystal-field and spin-orbit splitting of the uppermost valence band. The quaternary CuGaxInl-xSe2 system /7, 8 / allows tailoring of the optical bandgap for optimum solar energy conversion. By gradually substituting In by Ga the optical bandgap can be increased from 1.04 to 1.68 eV. In this note the optical absorption of CuGao. 251no. 75Se2 films is reported. Stoichiometric CuGaO. 251no. 75Se2 ingots, prepared b y vacuum fusion of the constituent elements (99.999 % p u r e) , were crushed and ground to 200 to 300 mesh powders. CuGa 0m251n0.75Se2 films of 1.0 pm thickness were prepared b y the flash evaporation technique onto Corning 7059 glass substrates at a pressure of 2~1 0-~ Torr. The temperature of the molybdenum source was kept around 1773 K and the evaporation rate was about 1 nm/s. The substrate temperature was kept at 623 K. 2 CuGaO. 251no. 75Se2 thin films formed at 623 K were polycrystalline and exhibited chalcopyrite structure with lattice parameters a = 0.5721 nm and c = 1.1489 nm, as seen from X-ray diffraction patterns. Thermoelectric power and Hall mobility measurements indicated p-type conduction in the films. The resistivity of the films, measured using the van der Pauw technique was in the range 100 to 150 Rcm. The composition of the films was measured by energy dispersive analysis of X-ray (EDAX) with an accuracy of i1 %. The calculated wt% of copper, gallium, indium,
Optical spectra and energy band structure of single crystalline CuGaS 2 and CuInS 2
Journal of Physics: Condensed Matter, 2007
The reflection spectroscopy of chalcopyrite CuGaS 2 and CuInS 2 single crystals has been applied for light polarized perpendicular (E ⊥ c) and parallel (E c) to the optical axis in the photon energy range between 1.5 and 6 eV at 77 K. By using the Kramers-Kronig relations, the spectral dependences of the real ε 1 and imaginary ε 2 components of the complex dielectric function ε(E) = ε 1 (E) + iε 2 (E) have been calculated for the investigated materials. As a result, the energy band structure of CuGaS 2 and CuInS 2 at photon energies higher than the fundamental band gap is derived from the analysis of the structures observed in ε(ω) spectra. Additionally, the spectral dependences of the complex refractive index, extinction coefficient and absorption coefficient s of CuGaS 2 and CuInS 2 single crystals are determined in the 1.5-6 eV photon energy range.
Crystal growth and investigation of the solid solutions of the system CuGe2P3-I2-IV-VI3
Materials Research Bulletin, 1990
The compounds Cu2GeS 3, Cu2SiS 3 and Cu2SiSe 3 were dissolved in the ternary compound CuGe2P 3. A modified Bridgman technique was used in the preparation, and good quality single crystals were grown for single phase samples. A complete solid solution for the system CuGe2P3-Cu2GeS 3 was found, with lattice parameters changing from 5.3678~ to 5.2895~ for 90% CuGe2P 3 and obeying Vegards law. In the CuGe2P3-Cu2GeSe 3 system the existence of the solid solution appears in the region of 0.25~x~0.9 when x is CuGe2P 3. However, the compound CuGe2P 3 does not form any solid solution with the compounds Cu2SiS 3 and Cu2SiSe 3.
Optical properties of cubic-phase Cu2GeSe4 single crystal
Journal of Applied Physics, 2013
We report optical properties of bulk Cu 2 GeSe 4 single crystal. X-ray powder diffraction measurement shows that this ternary compound forms in the cubic crystal structure and its lattice parameter is 5.5815(3) Å . Spectroscopic ellipsometric measurements are performed from 1.0 to 8.5 eV with the crystal at room temperature. Dielectric function e ¼ e 1 þ ie 2 , complex refractive index N ¼ n þ ik, normal incidence reflectivity R, and absorption coefficients a of Cu 2 GeSe 4 are obtained by modeling the ellipsometric data. The vibrational properties of Cu 2 GeSe 4 are characterized by Raman scattering spectroscopy. The data show four major optical structures whose spectral positions are accurately determined by analyzing the spectra with multiple Gaussian-Lorentzian mixed line profiles. V C 2013 AIP Publishing LLC.
Analysis of the edge emission of highly conductive CuGaTe2
Thin Solid Films, 2007
Low temperature photoluminescence of CuGaTe 2 was studied using number of different samples. Totally 11 photoluminescence bands were detected in the edge emission region. It is shown that at least 6 bands have peak positions at higher energy than the lowest optical bandgap of CuGaTe 2 . These bands were explained by using a model of resonant acceptor states (Fano-type resonances) in the valence band of CuGaTe 2 . Thus, the electron from the conduction band or from the donor level recombines with holes from acceptor levels related to the different valence bands. The energetic distance between these valence bands is found to be 84 meV.