Motivation Semiconducting GeSn alloy, because of tunable bandgap [1] and possibility of high electron and hole mobility [2] offers exciting avenues for bandgap and strain engineering in a silicon compatible technology [3] (Fig.

Metal-induced-gap-states model for Fermi-level pinning in metal-semiconductor contacts has been extended to metal-interfacial layer (IL)-semiconductor (MIS) contacts using a physics-based approach. Contact resistivity simulations evaluating various ILs on n-Ge indicate the possibility of forming low resistance contacts using TiO2, ZnO, and Sn-doped In2O3 (ITO) layers. Doping of the IL is proposed as an additional knob for lowering MIS contact resistance. This is demonstrated through simulations and experimentally verified with circular-transfer length method and diode measurements on Ti/n+-ZnO/n-Ge and Ti/ITO/n-Ge MIS contacts.

Metal contacts to n-type Ge have poor performance due to the Fermi level pinning near the Ge valence band at metal/Ge interfaces. The electron barrier height can be reduced by inserting ultrathin dielectrics at the metal-semiconductor interface. However, this technique introduces tunneling resistance from the large conduction band offset (CBO) between the insulator and Ge. In this work, the CBO between TiO2 and Ge is estimated to range from −0.06 to −0.26 eV so tunneling resistance can be reduced. By inserting 7.1 nm TiO2 between Al and n-Ge, current densities increased by about 900× at 0.1 V and 1200× at −0.1 V compared to contacts without TiO2.

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