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) Å, b=12.1593(4) Å, c=6.6084(3) Å, 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 is explained as due to the thermally activated hopping transport. From the analysis of the optical absorption spectra at room temperature, the fundamental energy gap was determined to be 0.843 eV. The photoconductivity spectra show the presence of a narrow band gap whose main peak is observed at 0.771 eV. This band is attributed to a free-to-bound transition from the defect acceptor level to the conduction band. The origin of this acceptor state, consistent with the chemical composition of the samples and screening effects, is tentatively attributed to selenium interstitials.

The T(y) phase diagram of the alloys CuInyGa1−ySe2, prepared by the chemical vapor deposition method, is obtained from X‐ray diffraction and differential thermal analyses. It is found that in addition to the chalcopyrite structure, a zincblende In2Se3‐rich phase and a zincblende Ga2Se3‐rich plus liquid two‐phase field, are obtained. Also it is found that the variation of the lattice parameter ratio c/a is not linear with composition but varies from 1.96 to 2.00 as y is increased from 0.0 to 0.6 and c/a being equal to 2.00 in the composition range 0.6 ⪅ y ⪅ 1.0. The energy gap values, obtained from optical absorption measurements, follow a second‐order equation in y giving a downward bowing parameter of about 0.15 eV.

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) Å for CuIn3Te5, and 5.9321(8) and 11.825(4) Å 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.

No abstract

No abstract