Two frequently observed problems with Schottky diodes are soft current–voltage characteristics and low avalanche breakdown voltages. These problems are sometimes found immediately upon fabrication, or they may develop during use. It is proposed that these phenomena can be explained by the existence of a thin layer (25–250 Å thick) between the metal and semiconductor which (i) has a high charge density, (ii) has a high trap density, and (iii) is conducting. Observed barrier height changes are explained by the trapping of charge carriers flowing through the layer and the lowered avalanche breakdown voltage by heating of carriers in the high field in the intervening layer. These explanations have been confirmed by measurements on GaP and GaAs diodes having a deliberately grown thin interfacial oxide ∠100 Å thick. Such an interfacial layer can be detected using a pulsed current–voltage technique described in the paper.
For nonlinear applications such as high‐speed switching, a device figure of merit is, γ, the ratio of the second derivative to the first derivative of the current‐voltage (I‐V) characteristic, or γ ≡ (d2I/dV2) (dI/dV). At room temperature, the value of γ for an ideal forward‐bias Schottky diode is about 40 V−1 It is shown that although the ideal reverse breakdown characteristic could give a value of γ greater than 40V−1 because of the statistical distribution of impurities, the effect of space‐charge resistance, and other complications, much lower values of γ are expected. Furthermore, the nonlinear characteristic is noisy, relatively slow, and causes some power consumption. It appears, therefore, that this nonlinearity is not likely to supersede Schottky barrier diodes in high‐speed switching applications. It does not, however, ride out the possibility of microwave generation application.
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