Defect-controlled conductivity in As2Se3 single crystals

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Abstract
The dark conductivity and thermoelectric power of As2Se3 single crystals have been studied between 250 and 460, and 320 and 460 K, respectively. Charge transport is by electrons. Their mobility is highly anisotropic, being more than one order of magnitude smaller for transport perpendicular to the layers. The results point to pinning of the Fermi level at 0·77 eV below the conduction band by intrinsic defects of high concentration. Among several bonding defects considered, antisite defects (threefold coordinated Se+ ions on As sites and twofold coordinated As+ ions on Se sites) seem most likely; these are responsible for the position of the Fermi level. Weak metastable interlayer bonds are proposed which can accommodate extra charge by bond switching reactions and which may also provide efficient recombination centres.