Growth and interfacial properties of epitaxial oxides on semiconductors: ab initio insights

Abstract

Crystalline metal oxides display a large number of physical functionalities such as ferroelectricity, magnetism, superconductivity, and Mott transitions. High quality heterostructures involving metal oxides and workhorse semiconductors such as silicon have the potential to open new directions in electronic device design that harness these degrees of freedom for computation or information storage. This review describes how first-principles theoretical modeling has informed current understanding of the growth mechanisms and resulting interfacial structures of crystalline, coherent, and epitaxial metal oxide thin films on semiconductors. Two overarching themes in this general area are addressed. First, the initial steps of oxide growth involve careful preparation of the semiconductor surface to guard against amorphous oxide formation and to create an ordered template for epitaxy. The methods by which this is achieved are reviewed, and possibilities for improving present processes to enable the epitaxial growth of a wider set of oxides are discussed. Second, once a heterointerface is created, the precise interfacial chemical composition and atomic structure is difficult to determine unambiguously from experiment or theory alone. The current understanding of the structure and properties of complex oxide/ semiconductor heterostructures is reviewed, and the main challenges to prediction-namely, (i) are these heterostructures in thermodynamic equilibrium or kinetically trapped, and (ii) how do the interfaces modify or couple to the degrees of freedom in the oxide?-are explored in detail for two metal oxide thin films on silicon. Finally, an outlook of where theoretical efforts in this field may be headed in the near future is provided.

Polarization that Holds Steady

“…In addition, in contrast to improper ferroelectrics, the primary order parameter of hyperferroelectrics couples directly to an applied electric field, which may allow for easier switching. Finally, ABC materials could be used to build an all-semiconducting ferroelectric field effect transistor, sidestepping many of the materials difficulties and interface effects that have hampered attempts to interface ferroelectric oxides with semiconductors [27][28][29]. TABLE II.…”

Theory of Ferroelectric ZrO2 Monolayers on Si

“…If successfully done, this enables the development of non-volatile devices such as ferroelectric field-effect transistors (FEFET). In a FEFET, the polarization of the oxide encodes the state of the device, and requires the application of a gate voltage only for switching the state, greatly reducing the power consumption and boosting the speed of the device [7,8]. Meeting this challenge requires a thin film ferroelectric oxide, as well as an atomically abrupt interface between the oxide and the semiconductor, so that the polarization of the oxide and the electronic states in the semiconductor are coupled.…”

“…An al-ternative approach is to search for materials such that, regardless of their bulk properties, they are stable in multiple polarization configurations as thin films [6]. The second requirement, i.e., an abrupt oxide-semiconductor interface, has been challenging due to the formation of amorphous oxides such as SiO 2 at the interface with a semiconductor such as Si [8,11,12]. This challenge has been overcome by using layer-by-layer growth methods such as molecular beam epitaxy (MBE) and employing highly controlled growth conditions [7,13,14].…”

Initial growth of Ba onGe(001): An STM and DFT study

“…In general, depending on the deposition temperature, there are two experimentally verified paths for creating the appropriate template on Si(001) [15,16]. At low temperatures (270−670 K) the motion of Si surface atoms is kinetically hindered and the deposition leads to the on-surface adsorption of the Sr or Ba adatoms.…”

“…At temperatures between 670 and 970 K, a new ordered (3 × 2) phase is formed at 1/6 ML, followed by the (2 × 1) reconstruction at 0.5 ML and the (3 × 1) phase near 1.0 ML. The phases on annealed Si(001) are predicted to be formed due to reorganization of the Si surface atoms and the formation of surface alloys [15,16].…”