Electrical properties of β-In2S3 thin films

Stoichiometric thin films of In2S3 were prepared by the thermal evaporation technique; the as-deposited films were non-crystalline and the crystallinity was built in on annealing at 423 K. The crystal structure as determined by both x-ray and electron diffraction showed that tetragonal films of beta-In2S3 phase were obtained. Both dark electrical resistivity rho and thermoelectric power (Seebeck coefficient S) were measured for films before and after annealing. The In2S3 films showed n-type conduction; the existence of two distinct activation energies Delta E-1 and Delta E-2 belongs to two types of level: a shallow level of Delta E-1 = 0.319 eV before annealing and Delta E-1 = 0.166 eV after annealing and deep levels of Delta E-2 = 0.61 eV for as deposited films and Delta E-1 = 0.515 eV for annealed film. The deep level was also detected by the space charge limited current technique and the trap density N-t is found to be 3.92 x 10(22) m(-3). The obtained results are explained on the basis of an energy diagram of beta-In2S3 proposed by Garlick.