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 ...

The dc voltage dependence of semiconductor grain‐boundary resistance

We have characterized the electrical transport properties of neutron‐transmutation‐doped polycrystalline silicon. Zero‐bias measurements of resistance have been made as a function of temperature on both bulk specimens and individual grain boundaries in this material. Below a doping level of ∼2×1015 phosphorus/cm3, the bulk resistance has a nearly Arrhenius behavior with an activation energy of ∼0.55 eV; above this donor concentration the resistivity is markedly curved on an Arrhenius plot with values of slope which decrease with decreasing temperature. Potential probe measurements show that a large spread in grain‐boundary impedances exist in these higher‐doped specimens. We compare our data to theoretical expressions for current flow across grain‐boundary potential barriers and good agreement is observed; these comparisons indicate that the largest grain‐boundary state densities observed in our samples consist of ∼6×1011 available single‐electron‐states/cm2 located within ∼0.2 eV from the center of the f...

Zero‐bias resistance of grain boundaries in neutron‐transmutation‐doped polycrystalline silicon

Thin‐film field‐effect transistors (FETs) have been prepared using poly(3‐hexylthiophene)/ arachidic acid and quinquethiophene/arachidic acid Langmuir–Blodgett (LB) films with thicknesses ranging from a monolayer to some ten monolayers. The effect of the number of layers on the mobility and conductivity has been studied. This is to our knowledge the first demonstration of a LB FET utilizing organic semiconductors as the active material.

Molecular field‐effect transistors using conducting polymer Langmuir–Blodgett films

Zero-bias resistance of grain boundaries in neutron transmutation doped polycrystalline silicon

The various theories of dc and ac conductivity in materials with hopping electronic charge carriers are critically examined in the light of the available experimental evidence. The temperature dependence of the dc conductivity suggests that in most materials the transition from nearest-neighbour hopping to variable-range hopping has been observed. However the theory in this region is insufficiently developed to enable meaningful determinations of the relevant parameters to be made from experimental data. The situation with ac theory is even less satisfactory, none of the existing theories being capable of accounting adequately for the observed behaviour. Neglect of many-body interactions and of the effect of the dielectric lattice, in addition to that of the charge carriers, are seen as the principal shortcomings. It follows, then, that the question of any relationship between the dc and ac conductivities cannot be answered at present, because of the lack of reliable data and because of insufficient theoretical understanding of the carrier processes in question.

M.L. Knotek

Papers

Temperature and thickness dependence of low temperature transport in amorphous silicon thin films: A comparison to amorphous germanium

Evidence for correlated hopping in impurity conduction at moderate impurity concentrations

The absence of a measurable hall effect in the superionic conductor RbAg4I5