C. Rincón

Crystal growth and structure, electrical, and optical characterization of the semiconductor Cu2SnSe3

X-ray powder diffraction by p-type Cu2SnSe3, prepared by the vertical Bridgman–Stockbarger technique, shows that this material crystallizes in a monoclinic structure, space group Cc, with unit cell parameters a=6.5936(1) A, b=12.1593(4) A, c=6.6084(3) A, and β=108.56(2)°. The temperature variation of the hole concentration p obtained from the Hall effect and electrical resistivity measurements from about 160 to 300 K, is explained as due to the thermal activation of an acceptor level with an ionization energy of 0.067 eV, whereas below 100 K, the conduction in the impurity band dominates the electrical transport process. From the analysis of the p vs T data, the density-of-states effective mass of the holes is estimated to be nearly of the same magnitude as the free electron mass. In the valence band, the temperature variation of the hole mobility is analyzed by taking into account the scattering of charge carriers by ionized and neutral impurities, and acoustic phonons. In the impurity band, the mobility...

Raman spectra of the ordered vacancy compounds CuIn3Se5 and CuGa3Se5

The optical vibrational modes of the ordered vacancy compounds CuIn3Se5 and CuGa3Se5 have been obtained by Raman spectra at various temperatures. The totally symmetric A1 mode appears around 155 and 167 cm−1 in CuIn3Se5 and CuGa3Se5, respectively. All the lines observed, except the B1 modes, present a reduction in their frequencies by about 10% as compared to the corresponding values in the CuInSe2 and CuGaSe2 chalcopyrites. This is due to the presence in these compounds of an array of vacancies occupying particular sites in the cation sublattice. These tend to relax the stretching forces thus reducing the vibrational frequencies.

Defect physics of the CuInSe2 chalcopyrite semiconductor

Abstract The activation energies of acceptor E A and donor levels E D in the chalcopyrite compound CuInSe 2 are calculated by using a simpler model based in the effective-mass theory for the case of single, double and triple point defect centers. Despite of the simplicity of this model, it is found that the values of E A and E D thus calculated for shallow and deep levels are in reasonable agreement with those reported from the experimental data. In the case of not shallow donor levels values of E D in good agreement with these data are calculated by using the free electron mass m 0 instead of the effective electron mass. From the analysis of the results, most of these levels have been identified as due to the presence of several native point defects.

Temperature dependence of the optical energy gap and Urbach’s energy of CuIn5Se8

The optical properties of the ordered defect compound CuIn5Se8, which crystallizes in a hexagonal structure, have been studied by the absorption technique. The analysis of the data shows that the band gap energy EG varies from 1.23 to 1.13 eV between 10 and 300 K. It is found that the variation of EG with temperature is due to the contribution of both acoustic and optical phonons with a characteristic phonon energy of about 14 meV. The optical absorption coefficient just below the absorption edge varies exponentially with photon energy indicating the presence of Urbach’s tail. The phonon energy hνp associated with Urbach’s tail, which is found to be 53 meV, is higher than the highest optical phonon mode reported for this compound, which is about 29 meV. The origin of the additional energy is attributed to the contribution of localized modes produced by structural disorder of low energy formation. An empirical relation, also used earlier in the case of 1:1:2 and other ordered defect compounds of the 1:3:5 ...

Crystal growth and structural, electrical, and optical characterization of CuIn3Te5 and CuGa3Te5 ordered vacancy compounds

X-ray powder diffraction studies of ordered vacancy compounds CuIn3Te5 and CuGa3Te5, prepared by the vertical Bridgman–Stockbarger technique, show that these materials exhibit a tetragonal chalcopyrite-related structure. The unit cell parameters a and c are, respectively, 6.1639(3) and 12.346(2) A for CuIn3Te5, and 5.9321(8) and 11.825(4) A for CuGa3Te5. From electrical resistivity characterization as a function of temperature a shallow acceptor level, with an activation energy lower than 30 meV, is found in both these compounds. Their direct energy gaps at room temperature are 1.013 and 1.092 eV for CuIn3Te5 and CuGa3Te5, respectively.

Crystal growth and structure of the semiconductor Cu2SnSe3

Abstract Bulk samples of Cu 2 SnSe 3 prepared by the vertical Bridgman–Stockbarger technique were studied by energy dispersive X-ray spectroscopy (EDX), X-ray powder diffraction and differential thermal analysis (DTA). It is observed that the chemical compositions of the samples used in the study were close to the ideal value 2:1:3. It is also found that Cu 2 SnSe 3 crystallizes in a monoclinic structure, space group Cc , with unit cell parameters a =6.5936(1) A, b =12.1593(4) A and c =6.6084(3) A and β =108.56(2)°. A secondary phase of SnSe 2 due to a eutectic reaction is also observed.

Optical properties and characterization of CuInSe2

Abstract CuInSe 2 single crystals grown from stoichiometric melts were studied by differential thermal analysis, X-ray diffraction, optical absorption and photoluminescence measurements. The resulting crystals were In-rich and exhibited n-type conductivity. From the optical measurements at low temperatures, a donor level around 12 meV and an acceptor level at about 40 meV, which have been attributed to indium atoms on copper sites and to copper vacancies respectively, appear as the predominant defect pair in our samples. Another defect level at about 70 meV, probably a donor level, has also been observed. Optical absorption measurements at room temperature show the presence of residual absorption, which has been attributed to direct-phononassisted transitions.

On the band gap anomaly in I–III–VI2, I–III3–VI5, and I–III5–VI8 families of Cu ternaries

The experimentally observed energy band gap difference (ΔE1) between the I–III3–VI5 and I–III–VI2 and the energy band gap difference (ΔE2) between the I–III5–VI8 and I–III–VI2 phases of Cu–In–Se, Cu–Ga–Se, Cu–In–Te, and Cu–Ga–Te systems is explained in terms of the relative shift of the conduction band minimum (CBM) and the valence band maximum (VBM) caused due to the presence of the ordered VCu and [In(Ga)Cu+2+2 VCu−1] defect pair and to the effect of the p–d hybridization. The nearly linear variation of ΔE1 and ΔE2 with p–d hybridization of the corresponding I–III–VI2 phase suggests that in selenides the lowering of the VBM predominates over that of the CBM. In the case of the Cu–In–Te system, they are very near the same magnitude, whereas in Cu–Ga–Te the lowering of the CBM predominates over that of the VBM.

Raman spectra of CuInTe2,CuIn3Te5, and CuIn5Te8 ternary compounds

From the analysis of Raman spectra, a comparative study of the lattice vibrational modes in CuInTe2, and of the ordered defect compounds (ODC) CuIn3Te5 and CuIn5Te8 of the Cu–In–Te system is reported. It is found that Raman lines in the ODCs appear at very nearly the same frequency as in CuInTe2. This is explained on the basis that the cation vacancy should not be considered merely as an empty site in the lattice but a localized region of positive Coulomb potential that attracts the valence electrons of the surrounding anions. It is proposed that the vacancy-Te force constant caused by the positive potential is of the same magnitude as in the Cu–Te stretching bond. The symmetry assignment of the observed lines is tentatively made by a comparative study of the vibrational modes of its binary analog Zn0.5Cd0.5Te, with phonon modes observed in CuInTe2 from polarized infrared optical measurements, and by estimating the modes frequency using several models reported in the literature for the chalcopyrite compou...

Luminescence and impurity states in CuInSe2

The photoluminescence spectrum of melt‐grown n‐CuInSe2 single crystal at 7 K, has been determined near the fundamental absorption edge. Three peaks, at approximately 0.980, 0.990, and 1.013 eV, have been observed. Considering the transition probabilities of recombination processes, donor‐to‐acceptor pair and the corresponding free‐to‐bound transitions have been identified. From the data, an absorption edge at (1.023±0.003) eV, a donor state at (10±2) meV, and an acceptor state at (33±2) meV have been determined.