Applied Surface Science, Vol.453, 48-55, 2018
Effective Schottky barrier height lowering technique for InGaAs contact scheme: D-MIGS and D-it reduction and interfacial dipole formation
The excellent Schottky barrier height (SBH) lowering effect of the metal/In0.53Ga0.47 As 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 In0.53Ga0.47 As surface, can be effectively alleviated, and the large SBH of the metal/In0.53Ga0.47 As 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 In0.53Ga0.47 As. 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 In0.53Ga0.47 As 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/In0.53Ga0.47 As 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(+)-In0.53Ga0.47 As (N-d = 1 x 10(19) cm(-3)) structure is estimated while the SBH of the Ti/ n(+)-In0.53Ga0.47 As structure is 0.27 eV. A specific contact resistivity value of (8.3 +/- 2.6) x 10(-9) Q cm(2) 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.