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Current–voltage (I–V) characteristics and their temperature dependence, of Schottky and metal-insulator-semiconductor diodes with tunnel thin insulating layers, are theoretically and experimentally studied. The effective barrier height of a Schottky diode becomes low and strongly dependent upon the applied voltage, when the impurity density of the semiconductor increases such that the tunnel current dominates the total curent. The I–V curves and their temperature dependence, of the tunnel thin MIS diodes strongly reflect the characteristics of the Schottky diodes, although the insulating layers suppress the currents, depending upon their I-layers thickness.

Schottky barrier heights of Ni/n-GaAs junctions were controlled by changing the pH of pretreatment chemicals. An effective barrier height of 0.8 eV was obtained by treatment with dilute HCl liquid (pH = l), and 0.6 eV by treatment with dilute NH4OH liquid (pH = 13). Surface analysis by an x-ray photoelectron spectroscopy indicated the existence of about twice the density of oxygen at the surface of the HCl-treated wafer as compared with that pretreated by the NH4OH liquid. The former shows nearly linear C -2–V characteristics, while the latter shows larger but less frequency dependent capacitances. Two levels of Ni/n-GaAs Schottky barriers were formed on a wafer by successive pretreatments and selective Ni evaporations.

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