Conduction mechanisms in amorphous and disordered semiconductors explained by a model of medium-range disorder of composition

Electronic structure, optical and photoelectrical properties of crystalline Si2Te3

“…The Urbach energy E U (Fig. 8) can serve as a measure of the absorption edge smearing, and accordingly, the measure of disorder degree [37], which, as indicated above, is determined by dynamic (temperature) and static (structural) disordering [34,38]:…”

Complex conductivity in the presence of long range potential fluctuations. Application to the determination of the gap state density in undoped and boron doped a-Si : H films grown by CVD

“…The existence of PF was first considered by Wannier [9] in insulators, by Shockley and Bardeen [10] in crystalline semiconductors, by Fritzsche [11] in amorphous semiconductors, and by Shklovskii and Efros [12,13] who have shown that randomly distributed donors and acceptors create large scale PF of magnitude comparable with the forbidden bandwidth. Pistoulet et al [14][15][16] derived general expressions of the dc transport coefficients by band carriers in the presence of PF ; dc conductivity activation energy and preexponential factor, photoconductivity, thermopower are drastically changed by PF. The expression of the complex conductivity 0'a, (,w, T) + i W Eac ('W, T) from dc to very high frequencies, when the effect of PF on band carriers is considered, was derived by Pistoulet, Roche, Abdalla [17] (PRA) ; the validity of the model was numerically confirmed by Soegandi, Roche, Pistoulet [18].…”

“…It has been shown [24] that the average charge density in a plane parallel to the surface of the sample is similar in both cases. Therefore, in field effect and in capacitance measurements, discrete levels in the presence of PF have the same effect as wide peaks in the absence of PF, as sketched in figure 2 of reference [14], so the effect of free carriers located in deep wells cannot be neglected. Similarly, transient capacitance spectroscopy and transient voltage spectroscopy only give access to average quantities ;…”

“…where P (Ec) is the probability of finding the band edge at energy Ec. As in previous papers [14,15,17], it is assumed that the non-uniform distribution of ionized centers (mainly shallow impurities) produces a Gaussian distribution of PF, of standard deviation r / J2, which has its maximum at some value .…”

AC FIELD AND FREQUENCY DEPENDENCE OF a-Si:H CONDUCTIVITY AT 4,2 K

“…(8), proposed an equivalent circuit consisting of two parallel RC circuits in series, the one representing the contact barrier, the other the bulk. We shall consider here that barriers separating potential wells may be located at the contact interfaces, and (or) in the bulk in presence of spatial fluctuations of potential (Pistoulet et al (11) ). In the simplest representation of this inhomogeneous medium, composed of stacked sheets, we consider potential hills of conductivity o occupying a fraction (1a) The experimental data may be well fitted by these expressions (Fig.…”