Grain boundary conductivity in different polycrystalline MoSe ₂ thin films

(Received 18 November 1993, revised 7 January 1994, accepted 17 January 1994)

Abstract
It has been shown early that curved plots for the conductivity of polycrystalline diselenide molybdenum were systematically obtained whatever the technique used for the obtention of the layers. In the general case of polycrystalline semiconductors these deviations from the simple thermoionic emission across the grain boundaries have been recently attributed to potential fluctuations at the grain boundaries. Here a good agreement between the experimental results and this new theory is obtained. The result deduced from theoretical propositions is conforted by the scanning electron micrographs of the layers and other preceeding experimental studies. In the light of the discussion of the MoSe ₂ layers, a quality factor Q is proposed for photovoltaic thin films. This estimation shows that the films obtained by solid state reaction and substitution are the best. Mo and Te thin films are sequentially deposited. Then an annealing under Se and Te pressure at 770 K for 24 h gives crystallized and stoichiometric MoSe ₂ thin films. These films have the higher quality factor among the films studied here (Q = 0.75). This is in close agreement with the good electrical and optical properties of these layers.