The dc voltage dependence of semiconductor grain-boundary resistance

Abstract

A model is developed to describe the potential barriers which often occur at grain boundaries in polycrystalline semiconductors. The resistance of such materials is determined by thermionic emission over these barriers. The dc grain-boundary current density as a function of applied voltage is calculated using several forms for the density of defect states within the boundary region. In all cases, the currents are Ohmic at low voltages; they can attain a quasisaturated level at intermediate voltages, and they display a sharp bias dependence at high voltages. The details of the intermediate and high-voltage characteristics are found to depend strongly on the grain-doping density and on the density and energy distribution of defect states at the grain boundary. Contrary to previous assertions, we find that the large current-voltage nonlinearities found in real materials are most likely associated with defect-state densities that decrease above the zero-bias Fermi level. The results of the model are compared with previous experimental data on Si and Ge bicrystals and on polycrystalline ZnO varistors. Finally, a detailed method for determining the energy density of grain-boundary defect states from current-voltage data is developed.

Non-linear current–voltage characteristics related to native defects in SrTiO3 and ZnO bicrystals

“…Non-linear I-V characteristics observed in SrTiO 3 and ZnO are often discussed in terms of DSB formed at their grain boundaries [6]. The barriers are considered to be generated by electrons trapped at interface states formed at grain boundaries.…”

“…Varistors are electric devices to protect electronic circuits, power lines and so on from surges or noises using an abrupt decrease of the resistivity at a critical voltage. The resistivity change is given by unique electrical properties of double Schottky barriers (DSB) formed at grain boundaries [6]. The current -voltage (I -V) characteristic across DSB exhibits non-linearity.…”

Identifying champion nanostructures for solar water-splitting

“…We hypothesized that high angle grain boundaries could decrease photocurrent in two ways: first, because these grain boundaries have a high concentration of interface states, they may act as recombination centers 30 ; second, the grain boundaries can generate a potential barrier that blocks majority carrier charge transport between adjacent crystals 31 . In the present materials the relatively small volume fraction of the hematite that is near a high angle grain boundaryi.e., within a typical diffusion and drift delivery length of 2 to 10 nm 32 -suggests that the first possibility does not explain most of the difference in photocurrent between 2L and 6L electrodes.…”

“…First, thermionic emission over potential barriers formed at high angle grain boundaries limits majority carrier transport 31 and, second, the potential drop at high angle grain boundary barriers decreases the potential that falls at the electrode-electrolyte interface. The first effect could limit current transport through large regions and effectively render them inactive for water splitting.…”

“…First, only the high angle grain boundaries parallel to the hematite-FTO interface will prevent current transport. Second, the magnitude of a potential barrier is a function of the interface state density and energy 31 : although most high angle grain boundaries have high densities of interface states, there may be a small proportion with relatively low concentrations of interface states 36 .…”