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

X-ray powder diffraction by p-type Cu2SnSe3, prepared by the vertical Bridg man-Stockbarger technique, shows that this material crystallizes in a monoc linic structure, space group Cc, with unit cell parameters a=6.5936(1) Angs trom, b=12.1593(4) Angstrom, c=6.6084(3) Angstrom, and beta =108.56(2)degre es. 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 th e impurity band dominates the electrical transport process. From the analys is 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 analyz ed by taking into account the scattering of charge carriers by ionized and neutral impurities, and acoustic phonons. In the impurity band, the mobilit y is explained as due to the thermally activated hopping transport. From th e analysis of the optical absorption spectra at room temperature, the funda mental energy gap was determined to be 0.843 eV. The photoconductivity spec tra 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 def ect acceptor level to the conduction band. The origin of this acceptor stat e, consistent with the chemical composition of the samples and screening ef fects, is tentatively attributed to selenium interstitials. (C) 2001 Americ an Institute of Physics.