Evidence for potential fluctuations in compensated amorphous silicon

Urbach-Martienssen Tails in the Absorption Spectra of Layered Ternary Semiconductor TlGaS2

“…As this particular behavior is so widely observed, it would appear that the origin of this effect is depending on a single universal mechanism. In spite of past extensive experimental [20][21][22][23][24][25] and theoretical [26][27][28][29][30][31][32][33][34][35][36][37] investigations, the microscopic origin of the absorption tail continues to be a matter of research. In crystalline lattices U-M tails originate from: (i) a temperature induced disorder reflecting the thermal occupancy of phonon states [20,26], (ii) temperature independent static structural disorder associated with impurities, dislocations, stacking faults, etc.…”

Transient photoconductivity studies of band tails states in compensated a-Si:H

“…The study of electronic transport in these materials has focused on fully-compensated a-Si:H where the Fermi energy remains close to that found in undoped material and the films are thus sufficiently insulating to allow direct mobility measurements to be performed using time-of-flight (TOF) experiments. TOF results for compensated a-Si:H [5][6][7][8][9][10] universally agree that the measured drift mobility of both electron and hole carriers systematically decrease as doping levels are increased. The reduction in mobility is furthermore accompanied by an increase in the associated mobility activation energy.…”

“…Despite the consensus in the experimental data, various physical explanations for the mobility phenomena have been proposed. These include an increase in the tail state density due to dopant related states [6,7], and a reduction in the extended state mobility due to dopant-induced potential fluctuations [8,9] although the fluctuation model appears to be inconsistent with the observed electric field dependence of TOF mobilities [10]. To further evaluate these possibilities, the present work presents transient photoconductivity (TPC) measurements for a series of compensated a-Si:H samples.…”

Photoconductivity of a-Si:H and a-Ge:H: influence of potential fluctuations

“…If the band edges are significantly modulated owing to electrostatic potential fluctuations, we should take into account the effect of such fluctuations (inhomogeneities) on charge transport. In fact, a number of papers have discussed the thermoelectric power [1,2], time of flight (TOF) [3][4][5], and ac transport [6,7], under the potential fluctuations.…”