Carrier transport across metalsemiconductor barriers
Abstract
Carrier transport across metalsemiconductor barriers has been studied theoretically and experimentally to give a generalized and quantitative presentation. The thermionic and tunneling processes have been analyzed in terms of accurate quantum transmission coefficients. The effects of imageforce lowering, temperature, and twodimensional statistical variation of impurity concentration have also been incorporated in the theory. Theoretical results give a description of the current transport, due to combined effect of tunneling and thermionic emission over a temperature range from essentially absolute zero to the highest practical temperatures, and over doping densities from 10 ^{14} cm ^{3} to complete degeneracy. An interesting result of the analysis is the existence of a minimum in the saturation current density J_{s} near 10 ^{16} cm ^{3}; the current density rises slightly at lower dopings because of enhanced transmission coefficient for thermionic emission and increases drastically at higher dopings because of tunneling. For example for PtSiSi system at 300°K with a barrier height of 0.85 eV, J_{s} is 80 nA/cm ^{2} at 10 ^{14} cm ^{3}, reaches a minimum of 60 nA/cm ^{2} at 10 ^{16} cm ^{3}, then rapidly increases to 10 ^{3} A/cm ^{2} at 10 ^{20} cm ^{3}. In the high doping range the average saturation current density is considerably increased by the effect of twodimensional impurity variation. The roomtemperature transition doping for breakdown in metalsilicon systems occurs at 8×10 ^{17} cm ^{3}; for lower dopings the breakdown is due to avalanche multiplication, and for higher dopings it is due to tunneling of carriers from the metal Fermi level to semiconductor bands. The metalsilicon diodes were fabricated by planar technology with guardring structures to eliminate edge effects. Extensive experimental studies, including currentvoltage, capacitancevoltage, and photoelectric measurements covering the doping range from 10 ^{14} to 10 ^{20} cm ^{3} and the temperature range from 77°K to 373°K, gave good agreement with theoretical predictions.
 Publication:

Solid State Electronics
 Pub Date:
 June 1970
 DOI:
 10.1016/00381101(70)900602
 Bibcode:
 1970SSEle..13..727C