The Effect of Interfacial Dipoles on the Metal-Double Interlayers-Semiconductor Structure and Their Application in Contact Resistivity Reduction

We demonstrate the contact resistance reduction for III–V semiconductor-based electrical and optical devices using the interfacial dipole effect of ultrathin double interlayers in a metal-interlayers-semiconductor (M-I-S) structure. An M-I-S structure blocks metal-induced gap states (MIGS) to a sufficient degree to alleviate Fermi level pinning caused by MIGS, resulting in contact resistance reduction. In addition, the ZnO/TiO 2 interlayers of an M-I-S structure induce an interfacial dipole effect that produces Schottky barrier height (Φ B ) reduction, which reduces the specific contact resistivity (ρ c ) of the metal/n-type III–V semiconductor contact. As a result, the Ti/ZnO(0.5 nm)/TiO 2 (0.5 nm)/n-GaAs metal-double interlayers-semiconductor (M-DI-S) structure achieved a ρ c of 2.51 × 10 –5 Ω·cm 2, which exhibited an ∼42 000× reduction and an ∼40× reduction compared to the Ti/n-GaAs metal-semiconductor (M-S) contact and the Ti/TiO 2 (0.5 nm)/n-GaAs M-I-S structure, respectively. The interfacial dipole at the ZnO/TiO 2 interface was determined to be approximately −0.104 eV, which induced a decrease in the effective work function of Ti and, therefore, reduced Φ B . X-ray photoelectron spectroscopy analysis of the M-DI-S structure also confirmed the existence of the interfacial dipole. On the basis of these results, the M-DI-S structure offers a promising nonalloyed Ohmic contact scheme for the development of III–V semiconductor-based applications.