High-k/metal gates on alternative channel materials, such as InGaAs with inherently higher electron mobility than silicon, are significant for complementary metal-oxide-semiconductor (CMOS) devices beyond the 15nm-node technology. Achieving Fermi level unpinning in both interfaces of high-k dielectric/metal gate and high-k dielectric/InGaAs is a must to realize the advanced CMOS devices. Previously, well-behaved capacitance-voltage (C-V) characteristics of both Al2O3/ Ga2O3 (Gd2O3) [GGO]/n- and p-In0.2Ga0.8As MOS capacitors (MOSCAPs) have been demonstrated with a low interfacial density of states (Dit). In addition, using metal gates of various work function values, small differences between theoretical and measured flat-band voltages (Vfb) were observed, suggesting a high degree of Fermi-level movement efficiency at the metal/Al2O3 and the GGO/n- and p-In0.2Ga0.8As interfaces.
In this work, the effective work function values of various metal gates, which include Al, Ti, Ni, Au, Pt, and TiN, have been extracted from the corresponding capacitance-voltage characteristics on the structure of Al2O3/GGO/InGaAs. The pinning strength value (S) of metal/oxide interface was then derived to be 0.99±0.11, which reveals the nearly unpinned Fermi level at the metal/oxide interface. Combining the unpinned metal/oxide and GGO/InGaAs interface, the metal /Al2O3/GGO/InGaAs hetero-structure can be readily employed in advanced InGaAs MOSFETs.

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