Space-charge-limited current, trap distribution and optical energy gap in amorphous (ln13Se87 and In20Se80) thin films

This paper shows that In13Se87 and In20Se80 thin films can be prepared by thermal evaporation technique. Current density-voltage (J-V) characteristics and thermally stimulated currents have been obtained. Coplanar silver electrodes were used. At low voltages, the current density behavior suggests ohmic conductivity, while at higher voltages, a region of space-charge-limited current conduction was observed. The analysis of the temperature dependence of J-V curves yields the following parameters: barrier height (b) energy of activation trap Et, trapping factor 0, trap density N-t, and concentration of the free carriers, no. The transition from ohmic to square law behavior was used to calculate all of these parameters. It was found that by increasing the In at% the trap density increased from 1.62 x 10(15) to 3.12 x 10(17) cm(-3) and the trap activation energy E-t, increases from 0.062 to 0.087eV. The optical absorption of these films was studied in the UV-VIS spectral range and the value of the optical energy gap was determined. The results of changes in the J-V characteristics and optical energy gap are discussed using a simple consideration, based on average coordination numbers, cohesive energy and bond energies. (C) 2002 Published by Elsevier Science Ltd.