Journal of Modern Physics, 2012, 3, 517-520 http://dx.doi.org/10.4236/jmp.2012.37070 Published Online July 2012 (http://www.SciRP.org/journal/jmp) Variable Range Hopping in Hydrogenated Amorphous Silicon-Nickel Alloys Abdelfattah Narjis 1 , Abdelhamid El Kaaouachi 1* , Abdelghani Sybous 1 , Lhoussine Limouny 1 , Said Dlimi 1 , Abdessadek Aboudihab 1 , Jamal Hemine 2 , Rachid Abdia 1 , Gerard Biskupski 3 1 Research Group ESNPS, Physics Department, Faculty of Sciences, University Ibn Zohr, Agadir, Morocco 2 Laboratoire de Physique de la Matière Condensée, Département de Physique, Faculté des Sciences et Techniques de Mohammadia, Mohammedia, Morocco 3 Laboratoire de Spectroscopie Hertzienne (LSH), Université des Sciences et Technologies de Lille I, Villeneuve d’Ascq, France Email: * kaaouachi21@yahoo.fr Received September 12, 2011; revised October 11, 2011; accepted November 12, 2011 ABSTRACT On the insulating side of the metal-insulator transition (MIT), the study of the effect of low Temperatures T on the elec- trical transport in amorphous silicon-nickel alloys a-Si 1–y Ni y :H exhibits that the electrical conductivity follows, at the beginning, the Efros-Shklovskii Variable Range Hopping regime (ES VRH) with T −1/2 . This behaviour showed that long range electron-electron interaction reduces the Density of State of carriers (DOS) at the Fermi level and creates the Coulomb gap (CG). For T higher than a critical value of temperature T C , we obtained the Mott Variable Range Hopping regime with T −1/4 , indicating that the DOS becomes almost constant in the vicinity of the Fermi level. The critical tem- perature T C decreases with nickel content in the alloys. Keywords: Amorphous Silicon-Nickel Alloys a-Si 1–y Ni y :H; Variable Range Hopping Conductivity; Transport Phenomenon; Metal Insulator Transition 1. Introduction Experimental results on resistivity in amorphous silicon- nickel alloys a-Si 1–y Ni y :H at low temperature, have been analysed in the insulating side of the Metal-Insulator Transition (MIT). The resistivity measurements were obtained for the insulating samples, Si 0.85 Ni 0.15 :H and Si 0.83 Ni 0.17 :H, in the range of temperature 1 - 140 K. The samples were prepared by radio-frequency sput- tering from silicon target. The subtracts (Corning 7059 glass) were at room temperature during deposition and the sputtering gaz was a 90% Ar and 10% H 2 . The hy- drogen was added to saturate silicon dangling bonds that might caused by the disorder. Compositions of the samples were determined by en- ergy dispersive analysis with x-rays (EDAX). Film thick- ness which were about 1 µm, were measured to an accu- racy of 0.1 µm using a Talysurf stylus. The amorphous nature was demonstrated by electron diffraction meas- urements in a transmission electron microscope. For the sample Si 0.83 Ni 0.17 :H, the electrical resistivity was measured using standard four-terminal AC tech- niques. However, this method gave rise to very long out of phase signal in the sample the most resistive (i.e., Si 0.85 Ni 0.15 :H), why the measurements were made using four-terminal DC technique . It is known that the Variable Range Hopping (VRH) conductivity of the three dimensional disordered systems, was shown by Mott [1,2] to behave like Ln(σ)α(T/T 0 ). This dependence was obtained by optimizing the hopping probability and assuming a slowly varying Density of State (DOS) in the vicinity of the Fermi level. On the contrary, Efros and Shklovskii (ES) [3,4] have predicted that long range electron-electron interaction reduces the DOS at the Fermi level and creates a soft Coulomb Gap (CG), which takes the form N(E)α(E − E F ) ν , with ν = 2. The existence of the CG leads to the ES VRH regime of the conductivity, which is written:   0 0 exp p T T       (1)   With p = (ν + 1)/(ν + 4) is an exponent that allows to conclude the profile of the DOS. In fact, Equation (1) remains quite universal since, when ν = 0, the DOS is constant and p = 0.25, corresponding to the Mott regime. But when ν = 2, the DOS varies in the vicinity of the * Corresponding author. Copyright © 2012 SciRes. JMP