Temperature-dependent Hall measurements have been performed on thin films of the ternary chalcopyrite CuGaSe 2 . Unintentionally doped samples and Na-containing samples are compared, as well as epitaxial and polycrystalline ones. Acceptor activation energies and acceptor and donor densities are extracted. Activation energies as well as defect densities vary over a wide range. We demonstrate that all samples are dominated by the same defect with an activation energy of 150 meV in the infinite-dilution limit. It is shown that the degree of compensation increases with increasing acceptor density. Thus direct evidence of self-compensation by intrinsic defects is given. CuGaSe 2 containing Na shows the same defects as CuGaSe 2 without Na: thus, it can be excluded that the dominant effect of Na is the introduction of a new acceptor. In addition, reduced compensation due to Na is not found; the net doping increases in spite of an increased compensation.

Grain-boundary-limited transport in semiconducting SnO 2 thin films: Model and experimentsA recently developed model that unifies the ballistic and diffusive transport mechanisms is applied to the carrier transport across potential barriers at grain boundaries in microcrystalline semiconducting materials. In the unified model, the conductance depends on the detailed structure of the band edge profile and in a nonlinear way on the carrier mean free path. Equilibrium band edge profiles are calculated within the trapping model for samples made up of a linear chain of identical grains. Quantum corrections allowing for tunneling are included in the calculation of electron mobilities. The dependence of the mobilities on carrier mean free path, grain length, number of grains, and temperature is examined, and appreciable departures from the results of the thermionic-field-emission model are found. Specifically, the unified model is applied in an analysis of Hall mobility data for n-type c-Si thin films in the range of thermally activated transport. Owing mainly to the effect of tunneling, potential barrier heights derived from the data are substantially larger than the activation energies of the Hall mobilities. The specific features of the unified model, however, cannot be resolved within the rather large uncertainties of the analysis.

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