Transport at the Epitaxial Interface between Germanium and Functional Oxides

Abstract

with reversible FE polarization.[ 9 ] Ponath et al. used a combination of impedance microscopy and piezoelectric scanning probe techniques to demonstrate the ferroelectric fi eld effect on charge modulation in the semiconductor, [ 10 ] highlighting the potential of these materials for FE fi eld effect devices.Owing to considerable challenges with the thermodynamic and chemical stability of oxide-semiconductor interfaces, [ 11 ] only a handful of perovskite oxides can be grown directly on semiconductors while maintaining high crystalline quality and an abrupt interface. [ 6,7,[12][13][14] These oxides can therefore be used as templates for the growth of other functional oxides, providing a route for extending the scope of possibilities for the integration of functional oxide phenomena with semiconductors. For example, ferroelectricity has been demonstrated for BTO [ 15 ] and Pb(Zr,Ti)O 3[ 16 ] grown on STO-templated GaAs; 2D electron gases have been demonstrated using LaTiO 3 [ 17 ] and GdTiO 3 [ 18,19 ] grown on STO-templated Si; magnetic functionality has been demonstrated with epitaxial multiferroic nanocomposites grown on STO-templated Si; [ 20 ] and optical modulators have been demonstrated with FE-BTO on STOSi. [ 21 ] Recent improvements in the crystalline quality of oxides grown on Ge using atomic layer deposition [ 22,23 ] further highlight the potential of a scalable integration route of functional oxides for microelectronics technology.Some applications, such as fi eld effect devices, require an insulating semiconductor-oxide interface for device operation. [ 6,13 ] Other oxide functionalities require current transfer with the semiconductor in order to fully realize their potential. Examples for oxide functionalities that can benefi t from interfacing with semiconductors via current transport include photoelectrocatalysis, [ 8 ] resistive switching, [ 24 ] and magnetic, [ 25 ] ferroelectric [ 26,27 ] and multiferroic [ 28 ] tunnel junctions. Interfacing directly with the semiconductor leads to simplifi ed circuits that employ these functionalities, and more importantly, to the development of new electronic and spintronic devices that combine the rich functionalities of oxides with standard devices such as fi eld effect transistors. Here, we develop an approach to control current transfer across an epitaxial oxide interface and focus on the fundamental electronic structure of the interface between BTO and Ge. First, the growth and structure of epitaxial BTO-Ge heterostructures is described, followed by a spectroscopic analysis of the interfacial band offsets and measurements of electronic transport across the interface.Combining functional oxides with conventional semiconductors provides the potential for transformational advancement of microelectronic devices. Harnessing the full spectrum of oxide functionalities requires current transport between the oxide and the semiconductor. This aspect is addressed by controlling the electronic barrier at an interface between a ferroelectric oxide, BaTiO 3 , and ge...

Epitaxial Oxides on Semiconductors: From Fundamentals to New Devices

“…This makes Ge a more feasible candidate for epitaxial high‐ k oxides compared to Si, though several challenges remain. The conduction band of STO (BTO) is below (aligned with) the conduction band of Ge . The absence of a barrier for electron transport facilitates some applications (e.g., Section ), but is detrimental for gate insulators.…”

Ab initio study of the BaTiO3/Ge interface

“…For the symmetric structure, however, the electron transfer to the electrode is more significant than the enhancement of the ionic polarization; therefore the band edges in BTO have an upward slope going from Ge to Au. The experimental studies on the BTO/Ge heterostructures have reported the conduction band edges to be approximately aligned [24,25], which suggests that the interfacial chemistry in these experimental systems is similar to the symmetric interface.…”

“…Researchers have reported studies of heterostructures involving BaTiO 3 and Ge [14,24,41] including BaTiO 3 thin films directly grown on Ge [25]. However, a study of the direct epitaxial BTO/Ge interface has only recently been published [1].…”

“…BaTiO 3 has been successfully grown on Si [7,21,22]; however in these studies SrTiO 3 has been used as a buffer layer due to the high lattice mismatch between Si and BTO of ∼ 4%. On the other hand, germanium closely matches the lattice constant of BTO within 1%, which has prompted many studies of BTO/Ge heterostructures [4,13,14,[23][24][25]. Some of these studies have included direct epitaxial interfaces between Ge and BTO without buffer layers; but a report on the atomic structure of this interface has only recently been published [1].…”

Toward the Atomically Abrupt Interfaces of SiOx/Semiconductor Junctions

“…Semiconductor devices, such as transistors, solar cells, LEDs, laser diodes, and sensors usually consist of a stack of an oxide film and a semiconductor crystal even though the oxide film is not grown on purpose (semiconductor surface parts become at least oxidized during the component manufacturing) . One of the most well‐known device examples is the metal‐oxide‐semiconductor field‐effect transistor.…”