The recent progress in ferroelectricity and antiferroelectricity in HfO2-based thin films is reported. Most ferroelectric thin film research focuses on perovskite structure materials, such as Pb(Zr,Ti)O3, BaTiO3, and SrBi2Ta2O9, which are considered to be feasible candidate materials for non-volatile semiconductor memory devices. However, these conventional ferroelectrics suffer from various problems including poor Si-compatibility, environmental issues related to Pb, large physical thickness, low resistance to hydrogen, and small bandgap. In 2011, ferroelectricity in Si-doped HfO2 thin films was first reported. Various dopants, such as Si, Zr, Al, Y, Gd, Sr, and La can induce ferro-electricity or antiferroelectricity in thin HfO2 films. They have large remanent polarization of up to 45 μC cm(-2), and their coercive field (≈1-2 MV cm(-1)) is larger than conventional ferroelectric films by approximately one order of magnitude. Furthermore, they can be extremely thin ( 5 eV). These differences are believed to overcome the barriers of conventional ferroelectrics in memory applications, including ferroelectric field-effect-transistors and three-dimensional capacitors. Moreover, the coupling of electric and thermal properties of the antiferroelectric thin films is expected to be useful for various applications, including energy harvesting/storage, solid-state-cooling, and infrared sensors.

Ferroelectricity and Antiferroelectricity of Doped Thin HfO2‐Based Films

The origin of the unexpected ferroelectricity in doped HfO2 thin films is now considered to be the formation of a non-centrosymmetric Pca21 orthorhombic phase. Due to the polycrystalline nature of the films as well as their extremely small thickness (∼10 nm) and mixed orientation and phase composition, structural analysis of doped HfO2 thin films remains a challenging task. As a further complication, the structural similarities of the orthorhombic and tetragonal phase are difficult to distinguish by typical structural analysis techniques such as X-ray diffraction. To resolve this issue, the changes in the grazing incidence X-ray diffraction (GIXRD) patterns of HfO2 films doped with Si, Al, and Gd are systematically examined. For all dopants, the shift of o111/t101 diffraction peak is observed with increasing atomic layer deposition (ALD) cycle ratio, and this shift is thought to originate from the orthorhombic to P42/nmc tetragonal phase transition with decreasing aspect ratio (2a/(b + c) for orthorhombic and c/a for the tetragonal phase). For quantitative phase analysis, Rietveld refinement is applied to the GIXRD patterns. A progressive phase transition from P21/c monoclinic to orthorhombic to tetragonal is confirmed for all dopants, and a strong relationship between orthorhombic phase fraction and remanent polarization value is uniquely demonstrated. The concentration range for the ferroelectric properties was the narrowest for the Si-doped HfO2 films. The dopant size is believed to strongly affect the concentration range for the ferroelectric phase stabilization, since small dopants can strongly decrease the free energy of the tetragonal phase due to their shorter metal–oxygen bonds.

A comprehensive study on the structural evolution of HfO2 thin films doped with various dopants

A concise and factual abstract is required. The abstract should state briefly the purpose of the research, the principal results and major conclusions. An abstract is often presented separately from the article, so it must be able to stand alone. For this reason, References should be avoided, but if essential, then cite the author(s) and year(s). Also, non-standard or uncommon abbreviations should be avoided, but if essential they must be defined at their first mention in the abstract itself.

Physica. B, Condensed matter

Abstract The coupling between light and collective oscillations of free carriers at metallic surfaces and nanostructures is at the origin of one of the main fields of nanophotonics: plasmonics. The potential applications offered by plasmonics range from biosensing to solar cell technologies and from nonlinear optics at the nanoscale to light harvesting and extraction in nanophotonic devices. Heavily doped semiconductors are particularly appealing for the infrared spectral window due to their compatibility with microelectronic technologies, which paves the way toward their integration in low-cost, mass-fabricated devices. In addition, their plasma frequency can be tuned chemically, optically, or electrically over a broad spectral range. This review covers the optical properties of the heavily doped conventional semiconductors such as Ge, Si, or III–V alloys and how they can be successfully employed in plasmonics. The modeling of their specific optical properties and the technological processes to realize nanoantennas, slits, or metasurfaces are presented. We also provide an overview of the applications of this young field of research, mainly focusing on biosensing and active devices, among the most recent developments in semiconductor plasmonics. Finally, an outlook of further research directions and the potential technological transfer is presented.

/pdf/semiconductor-infrared-plasmonics-4q7d05x57q.pdf

Semiconductor infrared plasmonics

The ferroelectricity in fluorite oxides has gained increasing interest due to its promising properties for multiple applications in semiconductor as well as energy devices. The structural origin of the unexpected ferroelectricity is now believed to be the formation of a non-centrosymmetric orthorhombic phase with the space group of Pca2(1). However, the factors driving the formation of the ferroelectric phase are still under debate. In this study, to understand the effect of annealing temperature, the crystallization process of doped HfO2 thin films is analyzed using in situ, high-temperature X-ray diffraction. The change in phase fractions in a multiphase system accompanied with the unit cell volume increase during annealing could be directly observed from X-ray diffraction analyses, and the observations give an information toward understanding the effect of annealing temperature on the structure and electrical properties. A strong coupling between the structure and the electrical properties is reconfirmed from this result.

Effect of Annealing Ferroelectric HfO2 Thin Films: In Situ, High Temperature X-Ray Diffraction

Si-doped HfO2 was prepared by solid state synthesis of the starting oxides. Using Rietveld refinement of high resolution X-ray diffraction patterns, a substitutional limit of Si in HfO2 was determined as less than 9 at. %. A second phase was identified as Cristobalite (SiO2) rather than HfSiO4, the latter of which would be expected from existing SiO2-HfO2 phase diagrams. Crystallographic refinement with increased Si-dopant concentration in monoclinic HfO2 shows that c/b increases, while β decreases. The spontaneous strain, which characterizes the ferroelastic distortion of the unit cell, was calculated and shown to decrease with increasing Si substitution.

Crystal structure of Si-doped HfO2

The effect of thermal annealing on the net donor concentration and diffusion of Si in In0.53Ga0.47As is compared for electrically active layers formed by ion implantation versus molecular beam epitaxy (MBE). Upon thermal treatment at temperatures of 700 °C or higher for 10 min, both ion implanted and growth-doped substrates converge to a common net donor solubility. These results indicate that while MBE doped substrates typically exhibit higher active concentrations relative to implanted substrates, the higher active Si concentrations from MBE growth are metastable and susceptible to deactivation upon subsequent thermal treatments after growth. Active Si doping concentrations in MBE doped material and ion-implanted materials are shown to converge toward a fixed net donor solubility limit of 1.4 × 1019 cm−3. Secondary ion mass spectroscopy of annealed samples indicates that the diffusivity of Si in MBE doped substrates is higher than those of ion implanted substrates presumably due to concentration-depende...

Comparison of thermal annealing effects on electrical activation of MBE grown and ion implant Si-doped In0.53Ga0.47As

In contrast to prior reports, evidence of concentration-dependent diffusion is reported for Si implanted In0.53Ga0.47As. The Fickian and concentration-dependent components of diffusivities were extracted using the Florida object oriented process and device simulator. The migration energy for silicon diffusion in In0.53Ga0.47As was calculated to be 2.4 and 1.5 eV for the Fickian and concentration dependent components of diffusion, respectively. A lack of change in diffusivities at given anneal temperatures suggest that transient-enhanced diffusion has not occurred. Due to these findings, silicon diffusion at high doping concentrations (>1 × 1020 cm−3) should be better characterized and understood for future complimentary metal-oxide semiconductor applications.

Concentration-dependent diffusion of ion-implanted silicon in In0.53Ga0.47As

An overview of various processing and dopant considerations for the creation of heavily-doped n-InGaAs is presented. A large body of experimental evidence and theoretical prediction point to dopant vacancy-complexing as the limiting mechanism for electrical activation in heavily Si doped InGaAs and GaAs. Dopant incorporation techniques which require thermal treatment steps to move dopants onto lattice sites like ion implantation and monolayer doping exhibit stable activation up to a limit of ≈1.5 × 1019 cm−3. Growth-based dopant incorporation methods have shown much higher (5 × 1019 cm−3) active concentrations but these activate concentrations are shown in multiple studies to be metastable. Other device specific process-flow constraints with respect to modern CMOS devices which may make some means of dopant incorporation method, or species selection more appropriate for a given application are also discussed. © The Author(s) 2016. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium, provided the original work is properly cited. [DOI: 10.1149/2.0201605jss] All rights reserved.

https://iopscience.iop.org/article/10.1149/2.0201605jss/pdf

Review—Dopant Selection Considerations and Equilibrium Thermal Processing Limits for n+-In0.53Ga0.47As

The evolution of implant damage in InGaAs is studied for electrically active Si+ and isoelectronic P+ implants. Extrinsic loops formed by excess interstitials are shown to be less stable upon annealing for n-type Si+ implants relative to isoelectronic P+ implants. Damage created by P+ implants into heavily n-doped InGaAs is also shown to be less stable than damage created by P+ implants into unintentionally doped InGaAs indicating that the background doping concentration can significantly effect the evolution of implant damage upon annealing. Previous results have suggested that the electrical activation and diffusion behavior of n-type dopants, like Si in InGaAs, may be strongly influenced by vacancy concentration. TEM results in this study also suggest that heavy n-type doping in InGaAs results in the formation of a large population of vacancy defects that enhance the dissolution or inhibit formation of interstitial loops. © 2015 The Electrochemical Society. [DOI: 10.1149/2.0141604jss] All rights reserved.

Henry Aldridge

Papers

Crystal structure of Si-doped HfO2

Comparison of thermal annealing effects on electrical activation of MBE grown and ion implant Si-doped In0.53Ga0.47As

Concentration-dependent diffusion of ion-implanted silicon in In0.53Ga0.47As

Review—Dopant Selection Considerations and Equilibrium Thermal Processing Limits for n+-In0.53Ga0.47As

Fermi-Level Effects on Extended Defect Evolution in Si+ and P+ Implanted In0.53Ga0.47As