PHOTOCONDUCTIVITY IN TIN SULFIDE SINGLE-CRYSTALS

The photoconductivity spectral response was measured for SnS single crystals at different temperatures with polarized light with the plane of polarization parallel to the a- and b-crystallographic axes which lie in the plane of cleavage. The photoconductivity energy gap was determined from the spectral response by the Moss rule. The room temperature photoconductivity energy gap was found to be (1.161 +/- 0.031) eV and (1.139 +/- 0.015) eV for the a- and b-axes, respectively. The temperature dependence of the photoconductivity energy gap was found to be linear between 91 and 300 K with a negative temperature coefficient equal to -(0.37 +/- 0.01) meV/K for the b-axis. The results for the a-axis showed large discrepancy which was attributed to crystal lattice bending which was introduced during the cleavage process. The minority carriers lifetime was determined from the photoconductivity frequency response which was found to be characterized by two different lifetimes.