Current transport in metal-semiconductor-metal (MSM) structures

The current-voltage characteristics of a metal-semiconductor-metal structure (essentially two metal-semiconductor contacts connected back to back) have been studied based on the thermionic emission theory. When a uniformly doped semiconductor is thin enough that it can be completely depleted before avalanche breakdown occurs, the structure can exhibit many novel transport behaviors. Two outstanding features of the structure are that (1) a wide range of high-level injection of minority carriers can be achieved by varying the barrier heights of the two contacts and (2) the critical voltage at which the minority carrier injection increases rapidly can be varied by varying the semiconductor doping and thickness.

Experimental silicon MSM structures of PtSi-Si-PtSi have been made from n-type silicon with doping of 4×10¹⁴ cm⁻³ and thickness of 12 μm. The critical voltage at room temperature is about 30 V. The current increases over five orders of magnitude with only 10 per cent increase of the voltage. The above results and other measurements over wide temperature range do substantiate the theoretical predictions.