Effective Schottky barrier height lowering technique for InGaAs contact scheme: DMIGS and Dit reduction and interfacial dipole formation

Abstract

The excellent Schottky barrier height (SBH) lowering effect of the metal/In0.53Ga0.47As contact is demonstrated to achieve extremely low contact resistance for n-channel InxGa1−xAs-based devices. Severe Fermi-level pinning, caused by large amounts of metal-induced gap states (MIGS) and interface states at the In0.53Ga0.47As surface, can be effectively alleviated, and the large SBH of the metal/In0.53Ga0.47As interface can be significantly lowered by introducing a metal-interlayer-semiconductor (MIS) structure, with the insertion of an Al-doped ZnO (AZO)/Ge interlayer stack between the metal and the In0.53Ga0.47As. The AZO interlayer is used as a heavily doped interlayer to reduce the MIGS, decrease its tunneling thickness, and lower the SBH. Reduction of the interface states at the In0.53Ga0.47As surface is achieved by adopting an ultrathin Ge layer as the surface passivation layer. Furthermore, a favorable interfacial dipole is formed at the AZO/Ge/In0.53Ga0.47As interfaces, which induces further SBH lowering and reduction of the AZO tunneling thickness. A below zero effective SBH for a Ti/AZO (1.2 nm)/Ge (0.5 nm)/n+-In0.53Ga0.47As (Nd = 1 × 1019 cm−3) structure is estimated while the SBH of the Ti/n+-In0.53Ga0.47As structure is 0.27 eV. A specific contact resistivity value of (8.3 ± 2.6) × 10−9 Ω cm2 is achieved for the proposed MIS structure, which is one of the lowest reported values for ohmic contacts to date. This result suggests that the proposed MIS structure, incorporating the AZO/Ge interlayer stack, presents a promising ohmic contact technique for III–V compound semiconductor-based applications.