Transport Across Heterointerfaces of Amorphous Niobium Oxide and Crystallographically Oriented Epitaxial Germanium.

Author(s) Hudait, M.K.; Clavel, M.; Liu, J.S.; Ghosh, A.; Jain, N.; Bodnar, R.J.
Journal ACS Appl Mater Interfaces
Date Published 2017 Dec 13

Because of the high carrier mobility of germanium (Ge) and high dielectric permittivity of amorphous niobium pentoxide (a-Nb2O5), Ge/a-Nb2O5 heterostructures offer several advantages for the rapidly developing field of oxide-semiconductor-based multifunctional devices. To this end, we investigate the growth, structural, band alignment, and metal-insulator-semiconductor (MIS) electrical properties of physical vapor-deposited Nb2O5 on crystallographically oriented (100), (110), and (111)Ge epilayers. The as-deposited Nb2O5 dielectrics were found to be in the amorphous state, demonstrating an abrupt oxide/semiconductor heterointerface with respect to Ge, when examined via low- and high-magnification cross-sectional transmission electron microscopy. Additionally, variable-angle spectroscopic ellipsometry and X-ray photoelectron spectroscopy (XPS) were used to independently determine the a-Nb2O5 band gap, yielding a direct gap value of 4.30 eV. Moreover, analysis of the heterointerfacial energy band alignment between a-Nb2O5 and epitaxial Ge revealed valance band offsets (ΔEV) greater than 2.5 eV, following the relation ΔEV(111) > ΔEV(110) > ΔEV(100). Similarly, utilizing the empirically determined a-Nb2O5 band gap, conduction band offsets (ΔEC) greater than 0.75 eV were found, likewise following the relation ΔEC(110) > ΔEC(100) > ΔEC(111). Leveraging the reduced ΔEC observed at the a-Nb2O5/Ge heterointerface, we also perform the first experimental investigation into Schottky barrier height reduction on n-Ge using a 2 nm a-Nb2O5 interlayer, resulting in a 20× increase in reverse-bias current density and improved Ohmic behavior.

DOI 10.1021/acsami.7b06601
ISSN 1944-8252
Citation ACS Appl Mater Interfaces. 2017;9(49):4331543324.

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