Influence of the exchange reaction on the electronic structure of GaN / Al junctions

Ab-initio full-potential linearized augmented plane wave (FLAPW) calculations have been used to study the influence of the interface morphology and, notably, of the exchange reaction on the electronic properties of Al/GaN (100) interfaces. Although the detailed mechanism is not understood, the exchange reaction has been purported to influence the Schottky barrier height as a result of the formation of an interfacial GaxAl1−xN layer. In particular, the effects of interface structure (i.e. interfacial bond lengths, semiconductor surface po1 larity, and reacted intralayers) on the SBH at the Al/GaN (001) junction are specifically addressed. Thus, the electronic structure of the following atomic configurations have been investigated theoretically: (i) an abrupt, relaxed GaN/Al interface; (ii) an interface which 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-inducedgap-states (MIGS); therefore, the presence of a monolayer–thick interfacial alloy layer does not result in an enhanced bandgap near 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 line–up is not strongly dependent on the interface morphology changes studied. The p-type SBH is reduced by less than 0.1 eV if the GaN surface is Ga-terminated compared to the N-terminated one. Moreover, we show that both an ultrathin GaxAl1−xN (x = 0, 0.5) intralayer and a Ga↔Al atomic swap at the interface does not significantly affect the Schottky barrier height. PACS 71, 73, 73.40.Sx, 73.61.-r