Electron tunneling modified ideality factors at heterocontacts

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Abstract
The role of thermally assisted tunneling in highly doped anisotype heterojunctions is investigated by a method involving the measurement of temperature dependence of ideality factor β when this is significantly different from unity. First of all a straightforward computational method for obtaining theoretical β in GaAs is quoted and compared with similar values obtained by other means. Then the validity of the results its shown experimentally through a systematic comparison with Au-n GaAs Schottky diodes with majority charge carrier density in the range 1018-1019cm-3. Agreement is generally good, although a systematic ratio of about 1.2 between carrier density Nd, the only disposable constant in the theory, and that calculated from Hall values has to be accounted for by assuming this to represent the neglected scattering factor in the latter, although uncertainty in the best average effective mass to use also contributes. Finally, the theory is applied to anisotype heterojunctions, all on p+-GaAs substrates, and a variety of degrees of agreement noted. Quantitative agreement is found for specially prepared abrupt n(GaIn)As-p GaAs heterojunctions, confirming the predominance of thermally assisted tunneling of this type of substantially doped anisotype device.

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