Conduction band-edge States associated with the removal of d-state degeneracies by the Jahn-Teller effect

Abstract

X-ray absorption spectroscopy (XAS) is used to study band edge electronic structure of high-transition metal (TM) and trivalent lanthanide rare earth (RE) oxide gate dielectrics. The lowest conduction band d-states in TiO 2 , ZrO 2 and HfO 2 are correlated with: 1) features in the O K 1 edge, and 2) transitions from occupied Ti 2p, Zr 3p and Hf 4p states to empty Ti 3d-, Zr 4d-, and Hf 5d-states, respectively. The relative energies of d-state features indicate that the respective optical bandgaps, E opt (or equivalently, E g), and conduction band offset energy with respect to Si, E B , scale monotonically with the d-state energies of the TM/RE atoms. The multiplicity of d-state features in the Ti L 2 3 spectrum of TiO 2 , and in the derivative of the O K 1 spectra for ZrO 2 and HfO 2 indicate a removal of d-state degeneracies that results from a static Jahn-Teller effect in these nanocrystalline thin film oxides. Similar removals of d-state degeneracies are demonstrated for complex TM/RE oxides including Zr and Hf titanates, and La, Gd and Dy scandates. Analysis of XAS and band edge spectra indicate an additional band edge state that is assigned Jahn-Teller distortions at internal grain boundaries. These band edges defect states are electronically active in photoconductivity (PC), internal photoemission (IPE), and act as bulk traps in metal oxide semiconductor (MOS) devices, contributing to asymmetries in tunneling and Frenkel-Poole transport that have important consequences for performance and reliability in advanced Si devices.

Origin of Charge Density atLaAlO3onSrTiO3Heterointerfaces: Possibility of Intrinsic Doping

“…Electrical transport properties were measured ex situ with a Quantum Design physical properties measurement system using the van der Pauw geometry, taking appropriate precautions to avoid photoinduced carriers. NEXAS and vis-VUV-SE are described elsewhere [8,9].…”

Optical and structural characterization of thermal oxidation effects of erbium thin films deposited by electron beam on silicon

“…45 Such grain boundary defects have been assigned to Jahn-Teller term d-state splitting of bulk nanocrystallites. These reports appear consistent with the x-ray diffraction data showing the presence of erbium silicate nanocrystallites.…”

Band edge electronic structure of transition metal/rare earth oxide dielectrics

“…[4]. These include remote plasma-assisted chemical vapor deposition (RPECVD) for the TM elemental oxides, and reactive evaporation for the TM elemental and TM/RE complex oxides.…”

“…These assignments differentiate between intrinsic band edge states of the bulk oxide film with anti-bonding and localized d-character, and localized states of a different origin, in this instance, defect states postulated to be at grain boundaries of the nanocrystalline films. These assignments are based on comparisons between X-ray absorption spectroscopy (XAS) studies of core level absorptions in nano-crystalline HfO 2 , ZrO 2 and TiO 2 thin films, as well studies of band edge states by photoconductivity and spectroscopic ellipsometry [2][3][4]. The core level XAS transitions terminate in either empty Hf, Zr and Ti d-states for transitions in which the core levels are TM p-states, or molecular orbital states for transitions in which the core level state is the O 1s level.…”

“…This article focuses on non-crystalline Zr and Hf silicate pseudo-binary and pseudo-ternary alloys [4,5]. It identifies ways in which chemical phase separation, CPS and crystallization of the TM oxide chemically separated phases may be effectively eliminated in pseudo-ternary alloys such as: (i) Zr(Hf)O 2 -SiO 2 -Si 3 N 4 and (ii) Zr(Hf)O 2 -SiO 2 -Al 2 O 3 , provided that alloy compositions are controlled within relatively narrow limits.…”