Investigations into the anomalous characteristics of sputtered molybdenum-pilicon schottky barrier diodes

Mullins, Francis Howard (1975) Investigations into the anomalous characteristics of sputtered molybdenum-pilicon schottky barrier diodes. University of Southampton, Doctoral Thesis.

Abstract

Consistently anomalous characteristics have been observed for Schottky barriers produced by the deposition of molybdenum onto silicon using a process of cathode sputtering. It has been found that excess current flows for reverse bias and lo forward bias voltage whereas insufficient current flows when the forward bias voltage exceeds 310 millivolts. Measurement of the capacitance-voltage characteristics has indicated the presence of a high density of positive charge close to the metal-semiconductor interface under reverse bias conditions. The charge storage characteristics were compared with these of similar Schottky barriers incorporating evaporated gold or aluminium and the switching speed of the sputtered molybdenum devices was found to be much greater than that of the other two types. A theory of electron and hole trapping near the semiconductor surface has been proposed. The presence of a high density; of traps near the surface increases the potential gradient resulting in significant tunnelling of electrons through the barrier, thereby altering the effective barrier height. The effective barrier height is dependent upon the applied voltage and distortion of the current-voltage characteristic results. The capacitance-voltage characteristics are also distorted since the charge distribution is non-uniform. The theory of trapping appears to fit the measured characteristics very well when an exponential spatial distribution of traps is used. It is thought that such a distribution could result from damage to the semi conductor surface during the sputtering process.

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