Crystallisation of selenium thin films doped with iodine after evaporation

Amorphous selenium thin films deposited under vacuum have been doped with i odine either during or after crystallisation. It is shown that when the fil ms are first crystallised at 363 K for 6 h and then submitted to iodine atm osphere at 363 K for 1 h, the structural properties of the films are not mo dified while their conductivity increases by a factor of 8. Iodine atmosphe re induces post crystallisation of amorphous selenium films even at room te mperature by increasing the selenium atom mobility at the surface of the fi lms, which induces growth of crystalline spherulites. With annealing, when the heating rate is high (> 15 K/min), constraints appear in the films, the density of spherulites increases and the films are inhomogeneous. When the heating rate is small and constant (1 K/min) the interaction between iodin e and selenium takes place all over the sample and there is only a small de nsity of small spherulites, while the crystallisation of the whole sample i s more homogeneous. XPS and microprobe analysis that the iodine is equally repartitioned in the selenium film show it. Moreover there is a mixture of neutral iodine and I-3(-) as shown by XPS and Raman studies. The high cryst alline quality of the films can explain the high conductivity (> 10(-3) Ome ga(-1) cm(-1)) of these selenium doped films (C) 2000 Kluwer Academic Publi shers.