INFLUENCE OF THE EXCHANGE-REACTION ON THE ELECTRONIC-STRUCTURE OF GANAL JUNCTIONS/

Ab initio full-potential Linearized augmented plane-wave (FLAPW) calcu lations have been used to study the influence of the interface morphol ogy and, notably, of the exchange reaction on the electronic propertie s of Al/GaN (100) interfaces. Although the detailed mechanism is not u nderstood, the exchange reaction has been purported to influence the S chottky barrier height (SBH) as a result of the formation of an interf acial GaxAl1-xN layer. In particular, the effects of interface structu re (i.e., interfacial bond lengths, semiconductor surface polarity, an d reacted intralayers) on the SBH at the Al/GaN (001) junction are spe cifically addressed. Thus, the electronic structure of the following a tomic configurations have been investigated theoretically: (i) an abru pt, relaxed GaN/Al interface; (ii) an interface that has undergone one monolayer of exchange reaction; and interfaces with a monolayer-thick interlayer of (iii)ALN and (iv) Ga0.5Al0.5N. The exchange reaction is found to be exothermic with an enthalpy of 0.1 eV/atom. We find that the first few layers of semiconductor are metallic due to the tailing of metal-induced gap states; therefore, the presence of a monalayer-th ick interfacial alloy layer does not result in an enhanced band gap ne ar the interface. Intermixed interfaces are found to pin the interface Fermi level at a position not significantly different from that of an abrupt interface. Our calculations also show that the interface band lineup is not strongly dependent on the interface morphology changes s tudied. The p type SBH is reduced by less than 0.1 eV if the GaN surfa ce is Ga terminated compared to the N terminated one. Moreover, we sho w that bath an ultrathin GaxAl1-xN (x = 0, 0.5) intralayer and a Ga<-> Al atomic swap at the interface do not significantly affect the Schott ky barrier height.[S0163-1829(98)07335-4].