The Current-Voltage Characteristic of a Nickel to N-Type Silicon Junction

Abstract

Contacts between metals and semiconductors have been under investigation for many years because of the value of their asymmetric conduction properties in producing rectification. F. Braun was one of the earliest experimenters in this field, and his basic method of making point contact to various crystals with a fine metal wire was the subject of continued research and development. A theoretical model to explain the characteristics of such junctions was developed by W. Schottky, and subsequent experimental and theoretical investigators have adopted the term Schottky barrier to refer to his description of a bending of energy bands in a metal to semiconductor junction. Silicon, among other substances, became an important semiconductor for such investigations. The general acceptance of the concept of the Schottky barrier (with theoretical modifications by others, particularly J. Bardeen) provided the basis for further study of junction effects, and in particular applications of the theory of electron tunneling to the Schottky barrier are providing information about both the physical processes involved in tunneling and the properties of the semiconductors themselves. Among the present researchers in this field is Dr. E.L. Wolf of Eastman Kodak Research laboratories, who is using an improved method of junction preparation in gathering experimental data related to the phenomenon of electron tunneling in metal to semiconductor junctions. Most of Dr. Wolf's work has been done at liquid helium temperature (4.2oK). The project described in this paper was devised with the idea that informative complementary data could be provided by a study of the junctions at higher temperatures. As will be discussed later in the section an data reduction and analysis, the theory of Schottky barriers predicts a strong temperature dependence of the current through a metal-semiconductor junction, thus suggesting measurements over a wide range of temperature to test the validity of the theory. The current also depends on the applied voltage, and thus taking the current-voltage characteristic curve is also an appropriate basic approach. It will be seen that information about the effect of electron tunneling can also be inferred from such data. This paper will describe the preparation of a nickel to N-type silicon junction and the measurement of its I-V characteristic in the range from 4.20 K to room temperature (300 0 K). Following sections on sample preparation, low temperature apparatus, the I-V measurement circuit, and experimental procedure will be a brief discussion of the Schottky barrier theory to support the data reduction and analysis.

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