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/In _0.53 Ga _0.47 As contact is demonstrated to achieve extremely low contact resistance for n-channel In _x Ga _1−x As-based devices. Severe Fermi-level pinning, caused by large amounts of metal-induced gap states (MIGS) and interface states at the In _0.53 Ga _0.47 As surface, can be effectively alleviated, and the large SBH of the metal/In _0.53 Ga _0.47 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 In _0.53 Ga _0.47 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 In _0.53 Ga _0.47 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/In _0.53 Ga _0.47 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 ⁺ -In _0.53 Ga _0.47 As (N _d = 1 × 10 ¹⁹ cm ⁻³ ) structure is estimated while the SBH of the Ti/n ⁺ -In _0.53 Ga _0.47 As structure is 0.27 eV. A specific contact resistivity value of (8.3 ± 2.6) × 10 ⁻⁹ Ω 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.