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

Abstract

In the past, 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 . 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 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.

Effect of substrate temperature on the properties of vacuum evaporated indium selenide thin films

“…For example, other III-VI compounds, such as GaS and GaSe have been reported to crystallize in the β-and ε-polytypes [17], while MOCVD grown InSe films belong to the β-polytype with hexagonal unit cells [18]. According to our XRD results, the thermal evaporated InSe films belong to the β-polytype with hexagonal unit cells [9,19]. The average grain size of Poly-InSe film was determined using Debye -Sherrer's equation,…”

“…1 shows the XRD patterns of InSe films grown at room temperature (a) and at 400°C (b). It is seen that the film prepared at room temperature is amorphous in nature [9] and becomes polycrystalline possessing hexagonal structure when T sb is 400°C. Similar observation has been noticed by Jin-Ho Park et al [15].…”

“…In this work, we attempted to deposit the InSe films on the substrates, which were kept at a temperature T sb higher than that of previously studied. We could prepare hexagonal poly-InSe films at T sb = 400°C [9].…”

Raman Spectra of In0.30Se0.70Amorphous Films

“…Amorphous films of In 1-x Sex alloys within a broad x range are available by thermal vacuum evaporation [4,5]. These materials are interesting for their potential applications in photovoltaics and microelectronics [6].…”

Electrical Conductivity and Thermoelectric Power of a-Se80-xGa20Tex(x=0,5,10,15 and 20) Thin Films

“…The lattice perfection and the energy band gap of the material play a major role in the preparation of the device for a particular wavelength, which can be modified by the addition of dopants [22]. Several workers [23][24][25][26][27][28][29][30][31] have conducted electrical, structural, and optical studies of a-Se-Ga and other amorphous alloys.…”