Determination of the Density of States Distribution in the Energy Gap of a-Si:H (original) (raw)
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Changes in the electrical conductivity of amorphous semiconductors
Materials Chemistry and Physics, 1996
The changes in the electrical conductivity occurring in chalcogenide amorphous semiconductors, from the system GeSeTe, have been studied. This study includes the determination of I-V characteristics, the electrical conductivity and its relationship with temperature, and, finally, the ageing of samples started by annealing and by thermal switching due to Joule self-heating, To complete the analysis, the possible structural modifications which could have been produced during the experiments have been verified by means of X-ray diffraction.
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In this paper, we develop an approximate theory of the temperature coefficient of resistivity (TCR) and conductivity based upon the recently proposed Microscopic Response Method. By introducing suitable approximations for the lattice dynamics, localized and extended electronic states, we produce new explicit forms for the conductivity and TCR, which depend on easily accessible material parameters. The theory is in reasonable agreement with experiments on a-Si:H and a-Ge:H. A long-standing puzzle, a "kink" in the experimental log 10 σ vs. 1/T curve, is predicted by the theory and attributed to localized to extended transitions, which have not been properly handled in earlier theories.
Physical Review B, 2007
We present an ab initio calculation of the DC conductivity of amorphous silicon and hydrogenated amorphous silicon. The Kubo-Greenwood formula is used to obtain the DC conductivity, by thermal averaging over extended dynamical simulation. Its application to disordered solids is discussed. The conductivity is computed for a wide range of temperatures and doping is explored in a naive way by shifting the Fermi level. We observed the Meyer-Neldel rule for the electrical conductivity with EMNR=0.06 eV and a temperature coefficient of resistance close to experiment for a-Si:H. In general, experimental trends are reproduced by these calculations, and this suggests the possible utility of the approach for modeling carrier transport in other disordered systems.
Physical Review B
Unraveling the dominant charge transport mechanism in high-mobility amorphous oxide semiconductors is still a matter of controversy. In the present study we extended the random band-edge model suggested before for the charge transport and Hall-effect mobility in such disordered materials [Fishchuk et al., Phys. Rev. B 93, 195204 (2016)], and also describe the field-effect-modulated thermoelectricity in amorphous In-Ga-Zn-O (a-IGZO) films under the same premises. The model is based on the concept of charge transport through the extended states and assumes that the transport is limited by the spatial variation of the position of the band edge due to the disorder potential, rather than by localized states. The theoretical model is formulated using the effective medium approximation framework and describes well basic features of the Seebeck coefficient in disordered materials as a function of energy disorder, carrier concentration, and temperature. Carrier concentration dependencies of power factor and thermoelectric figure of merit have been also considered for such systems. Besides, our calculations reveal a remarkable turnover effect from a negative to a positive temperature dependence of Seebeck coefficient upon increasing carrier concentration. The suggested unified model provides a good quantitative description of available experimental data on the Seebeck coefficient and the charge mobilities measured in the same a-IGZO transistor as a function of the gate voltage and temperature by considering the same charge transport mechanisms. This promotes a deeper understanding and a more credible and accurate description of the transport process in a-IGZO films.
Electrical Conductivity of V2O5–TeO2–Sb Glasses at Low Temperatures
Journal of Electronic Materials, 2014
Semiconducting glasses of the type 40TeO 2-(60 À x) V 2 O 5-xSb were prepared by rapid melt quenching and their dc electrical conductivity was measured in the temperature range 180-296 K. For these glassy samples, the dc electrical conductivity ranged from 2.26 9 10 À7 S cm À1 to 1.11 9 10 À5 S cm À1 at 296 K, indicating the conductivity is enhanced by increasing the V 2 O 5 content. These experimental results could be explained on the basis of different mechanisms (based on polaron-hopping theory) in the different temperature regions. At temperatures above H D /2 (where H D is the Debye temperature), the non-adiabatic small polaron hopping (NASPH) model is consistent with the data, whereas at temperatures below H D /2, a T À1/4 dependence of the conductivity indicative of the variable range hopping (VRH) mechanism is dominant. For all these glasses crossover from SPH to VRH conduction was observed at a characteristic temperature T R £ H D /2. In this study, the hopping carrier density and carrier mobility were determined at different temperatures. N (E F), the density of states at (or near) the Fermi level, was also determined from the Mott variables; the results were dependent on V 2 O 5 content.