The influence of microcrystalline inhomogeneities embedded in amorphous InxSe100-x films on their electrical and optical properties

In the past, InxSe100-x amorphous layers have been described as n or p type according to their majority carriers. The majority carrier type varies from one study to another, even with films of the same composition, which is a very serious problem. In this paper we explain this discrepancy by demonstrating that microcrystallite inhomogeneities are present in the amorphous InxSe100-x. While x-ray diffraction patterns are typical of amorphous samples, the selected-area diffraction obtained using a transmission electron microscope depends on the area studied. It is shown that the layers are constituted of microcrystallites embedded in an amorphous matrix. Therefore the majority carrier type changes when the p-type nature of the amorphous matrix is masked by the n-type nature of the crystallites at the percolation threshold. Of course this percolation threshold depends not only on the composition of the layer but also on the deposition process, which explains the different majority carrier types found for identical composition The two critical temperatures measured from the conductivity curves can be attributed to the phase transition alpha-In2Se3 --> beta-In2Se3 of the microcrystallites (the first one) and the overall crystallization of the layer (the second one). The typical optical absorption and differential thermal analysis properties are explained in the same way.