Taizo Irie

Electrical Properties of p- and n-Type CuInSe2 Single Crystals

The electrical resistivity and Hall effect of p- and n-type CuInSe2 single crystals are measured in the temperature range from 80 K to 500 K. p- and n-type samples are prepared by doping with excess Se and excess In, respectively. The acceptor levels at 0.020 eV and 0.028 eV above the valence band and the donor levels at 0.012 eV and 0.18 eV below the conduction band are identified. The mobility data are analysed assuming scattering by acoustic, polar optical, and nonpolar optical phonons and by ionized impurities. For some of the n-type samples, the measurements are extended to liquid helium temperature and the result is analysed by the existing theories of impurity band conduction.

Transport properties of CdIn2S4 single crystals

Abstract Several transport properties have been studied on CdIn 2 S 4 single crystals with different degrees of deviation from stoichiometry. The energy gap at 0 K was determined from the electrical measurements to be 2.2 eV. The anisotropy of the magnetoresistance effect was found and it was suggested that the minima of the conduction band were located at points along the [100] directions in k space. From an analysis of the mobility data it was found that the high resistivity of the samples is due to compensation of donors by acceptors introduced by excess sulphur. Several band parameters, the carrier scattering mechanisms and the impurity levels were determined. The thermal conductivity was measured from 4 K to 300 K and analysed by Callaways formalism.

Raman-Scattering Properties of I-III-VI2 Group Chalcopyrite Semiconductors

The Raman-scattering spectra of I-III-VI2 group chalcopyrite semiconductors and their solid solutions were measured. The frequency relationship for the A1 vibrational mode agrees with the simple ratio of the anion atomic weights, although it also depends on the mean atomic weights of the cations. Compositional change of the A1 mode frequency for their solid solutions with anion substitution can be explained by the probability of formation of two pairs of anion atoms.

Optical and Electrical Properties of CuIn5S8 and AgIn5S8 Single Crystals

The energy gaps at 300 and 96 K of CuIn5S8 and AgIn5S8 single crystals were determined from the optical absorption measurements. The peaks of the photoconductive spectra observed at 300 and 77 K were in good agreement with the energy gaps. The resistivity and the mobility for the samples with less sulphur than the stoichiometric one were determined from the electrical measurements.

Preparation and some properties of CuInSe2 single crystals

Abstract A brief review of our previous research on the electrical properties and p-n junction characteristics of CuInSe2 single crystals prepared by the normal freezing method is presented. Recently the optical absorption spectra have been measured as functions of temperature and pressure. The temperature and pressure coefficients of the absorption edge are found to be −1.1 × 10 −4 eV K −1 and +2.8 × 10 −11 eV Pa −1 respectively. Some trends may be seen in the distribution of the absorption edge energies measured for various n- and p-type samples.

Influence of nonstoichiometry on the Urbach’s tails of absorption spectra for CuInSe2 single crystals

Optical absorption spectra of CuInSe2 single crystals were measured for the samples with −0.150≤x≤0.053, where x represents a degree of nonstoichiometry in the formula Cu1−xIn1+xSe2. The Urbach’s tail was observed for all samples between 90 K and room temperature. The Urbach’s energy, which represents an arbitrary intensity of exciton–phonon interaction, was almost constant for the Cu‐rich samples (x<0), while it increased with increasing In composition for the In‐rich ones (x≳0). Such an increase of the Urbach’s energy was explained to be due to enhanced electronic distortion caused by the compositional deviation from stoichiometry in terms of simultaneous influence of electron–phonon interaction and structural disorder.

Thermodynamical Properties of I-III-VI2-Group Chalcopyrite Semiconductors

Melting points and transition points of I-III-VI2-group compounds and their solid solutions were determined exactly. The heats of fusion and transition were also estimated. The melting points of I-III-VI2-group compounds and solid solutions depend on mean atomic weight and ionicity. It is found that the melting points are influenced by lattice strain. Heats of fusion and transition of I-III-VI2-group compounds depend on mean atomic weight, ionicity and u-parameter, the trends of which are in contrast to those for III-V-group compounds. Heats of fusion and transition of their solid solutions are much smaller than those for the end-member compounds.

Preparation and Characterization of Electrodeposited CuInSe2 Thin Films

CuInSe2 thin films were prepared on SnO2-coated glass by electrodeposition from aqueous solution containing CuCl2, InCl3 and SeO2. The deposition was carried out by varying cathode potential. It was found that the Cu/In ratio which influences CuInSe2 characteristics greatly can be controlled by the cathode potential. Annealing of as-deposited films in N2 atmosphere at 350°C was found to result in the formation of CuInSe2 films having a chalcopyrite structure. With the use of these annealed CuInSe2 thin films, CdS/CuInSe2 thin-film solar cells were formed as a preliminary step and the conversion efficiency of 1.49% was obtained.

Valence band densities of states of CdIn2S4 and In2S3 from x-ray photoelectron spectroscopy

Abstract X-ray photoelectron spectra of the valence band of CdIn 2 S 4 and In 2 S 3 single crystals have been measured. The spectrum of CdIn 2 S 4 has a strong resemblance to its synthesized spectrum from the In 2 S 3 and CdS spectra, which is in good agreement with the theoretical density of states (DOS). The contribution of constituent atoms to the valence band DOS in CdIn 2 S 4 is corresponding to those in In 2 S 3 and CdS.

Electronic structure of some I–III–VI2 chalcopyrite semiconductors studied by synchrotron radiation

Photoemission spectra were measured for the I–III–IV2 chalcopyrite semiconductors CuInSe2, CuInS2, CuInTe2, and CuGaS2 with various photon energies (32 to 140, and 1253 eV). The partial density‐of‐states (DOS) of Cu 3d orbital is selectively observed at the photon energies beyond 100 eV. The DOS of Cu 3d spreads from the top of valence band (VB) to 5 or 6 eV below. Three dominant peaks are labeled as A, B, and C, the structures of which are interpreted as antibonding, nonbonding, and bonding states. Reflection spectra were also measured for CuInSe2 from 2 to 100 eV at room temperature and 98.5 K. The In 4d core reflection is observed at 17.5, 18.9, 19.8, and 21.2 eV at 98.5 K; very similar characteristics are also observed at 5.28, 6.21, 7.35, and 8.67 eV. These contributions are due to the Cu 3d nonbonding electrons. Photoemission and reflection experiments thus confirm conclusively the existence of nonbonding Cu 3d states in I–III–VI2 chalcopyrites. This result proves the theoretical model that attribut...