THE FORMATION OF OHMIC AND SCHOTTKY ENHANCED CONTACTS TO III-V COMPOUND SEMICONDUCTORS VIA THE EXCHANGE MECHANISM - A COMBINED THERMODYNAMIC AND KINETIC-MODEL

A methodology is presented for altering the electrical properties of c ontacts to III-V compound semiconductors through the use of controlled interfacial chemical reactions. The process by which this is accompli shed has been termed the exchange mechanism. Under this mechanism, a m etallization consisting of a transition metal and a group III element (denoted TIII') is reacted with the semiconductor (denoted IIIV) in su ch a way that the group III elements of the metallization and substrat e, III' and III, are exchanged without the formation of any new phases . This leads to the creation of a ternary semiconductor alloy S, or II IXS'III1-XSV, at the contact interface, where X-S denotes the mole fra ction of III'V in the semiconductor alloy phase S. The electrical prop erties of the contact subsequent to the exchange reaction then corresp ond to those of a metal/IIIXS'III1-XSV interface. Moreover, by employi ng ternary metallizations of varying composition M, or TIIIXM'III1-XM (where X-M represents the mole fraction of TIII' within the ternary me tallic phase M), the resulting interfacial composition of the semicond uctor and hence the electrical properties of the contact may be varied in a systematic fashion. Rather stringent thermodynamic and kinetic c riteria must be met in order for the exchange reaction mechanism to be operative. These factors are described using a quantitative model. Th e limitations of applicability of the model are also discussed. (C) 19 98 American Institute of Physics. [S0021-8979(98)00720-8].