Matching Items (5)

129253-Thumbnail Image.png

Quasi-two-dimensional electron gas at the epitaxial alumina/SrTiO3 interface: Control of oxygen vacancies

Description

In this paper, we report on the highly conductive layer formed at the crystalline γ-alumina/SrTiO[subscript 3] interface, which is attributed to oxygen vacancies. We describe the structure of thin γ-alumina

In this paper, we report on the highly conductive layer formed at the crystalline γ-alumina/SrTiO[subscript 3] interface, which is attributed to oxygen vacancies. We describe the structure of thin γ-alumina layers deposited by molecular beam epitaxy on SrTiO3 (001) at growth temperatures in the range of 400–800 °C, as determined by reflection-high-energy electron diffraction, x-ray diffraction, and high-resolution electron microscopy. In situ x-ray photoelectron spectroscopy was used to confirm the presence of the oxygen-deficient layer. Electrical characterization indicates sheet carrier densities of ∼1013 cm−2 at room temperature for the sample deposited at 700 °C, with a maximum electron Hall mobility of 3100 cm[superscript 2]V[superscript −1]s[superscript −1] at 3.2 K and room temperature mobility of 22 cm[superscript 2]V[superscript −1]s[superscript −1]. Annealing in oxygen is found to reduce the carrier density and turn a conductive sample into an insulator.

Contributors

Agent

Created

Date Created
  • 2015-03-07

129317-Thumbnail Image.png

Carrier density modulation in a germanium heterostructure by ferroelectric switching

Description

The development of non-volatile logic through direct coupling of spontaneous ferroelectric polarization with semiconductor charge carriers is nontrivial, with many issues, including epitaxial ferroelectric growth, demonstration of ferroelectric switching and

The development of non-volatile logic through direct coupling of spontaneous ferroelectric polarization with semiconductor charge carriers is nontrivial, with many issues, including epitaxial ferroelectric growth, demonstration of ferroelectric switching and measurable semiconductor modulation. Here we report a true ferroelectric field effect—carrier density modulation in an underlying Ge(001) substrate by switching of the ferroelectric polarization in epitaxial c-axis-oriented BaTiO[subscript 3] grown by molecular beam epitaxy. Using the density functional theory, we demonstrate that switching of BaTiO[subscript 3] polarization results in a large electric potential change in Ge. Aberration-corrected electron microscopy confirms BaTiO[subscript 3] tetragonality and the absence of any low-permittivity interlayer at the interface with Ge. The non-volatile, switchable nature of the single-domain out-of-plane ferroelectric polarization of BaTiO[subscript 3] is confirmed using piezoelectric force microscopy. The effect of the polarization switching on the conductivity of the underlying Ge is measured using microwave impedance microscopy, clearly demonstrating a ferroelectric field effect.

Contributors

Agent

Created

Date Created
  • 2015-01-01

129606-Thumbnail Image.png

Epitaxy of polar semiconductor Co3O4 (110): Growth, structure, and characterization

Description

The (110) plane of Co[subscript 3]O[subscript 4] spinel exhibits significantly higher rates of carbon monoxide conversion due to the presence of active Co[superscript 3+] species at the surface. However, experimental

The (110) plane of Co[subscript 3]O[subscript 4] spinel exhibits significantly higher rates of carbon monoxide conversion due to the presence of active Co[superscript 3+] species at the surface. However, experimental studies of Co[subscript 3]O[subscript 4] (110) surfaces and interfaces have been limited by the difficulties in growing high-quality films. We report thin (10–250 Å) Co[subscript 3]O[subscript 4] films grown by molecular beam epitaxy in the polar (110) direction on MgAl[subscript 2]O[subscript 4] substrates. Reflection high-energy electron diffraction, atomic force microscopy, x-ray diffraction, and transmission electron microscopy measurements attest to the high quality of the as-grown films. Furthermore, we investigate the electronic structure of this material by core level and valence band x-ray photoelectron spectroscopy, and first-principles density functional theory calculations. Ellipsometry reveals a direct band gap of 0.75 eV and other interband transitions at higher energies. A valence band offset of 3.2 eV is measured for the Co[subscript 3]O[subscript 4]/MgAl[subscript 2]O[subscript 4] heterostructure. Magnetic measurements show the signature of antiferromagnetic ordering at 49 K. FTIR ellipsometry finds three infrared-active phonons between 300 and 700 cm[superscript −1].

Contributors

Created

Date Created
  • 2014-06-28

129617-Thumbnail Image.png

Epitaxial Zintl aluminide SrAl4 grown on a LaAlO3 substrate

Description

Zintl phases are a class of intermetallic materials that have simultaneously ionic and covalent bonding resulting from charge transfer between two different atomic species. We present a combined first principles

Zintl phases are a class of intermetallic materials that have simultaneously ionic and covalent bonding resulting from charge transfer between two different atomic species. We present a combined first principles and experimental study of Zintl-phase SrAl4, which is grown in thin film form on the perovskite oxide LaAlO3 using molecular beam epitaxy. The structural properties are investigated using reflection-high-energy electron diffraction, x-ray diffraction, and cross-section transmission electron microscopy, which reveal relaxed epitaxial island growth. Photoelectron spectroscopy measurements verify the Zintl-Klemm nature of the bonding in the material and are utilized to determine the band offset and the work function of SrAl4, while transport measurements confirm its metallic behavior. The experimentally observed properties are confirmed using density functional calculations.

Contributors

Agent

Created

Date Created
  • 2013-07

129205-Thumbnail Image.png

Atomic layer deposition of crystalline SrHfO3 directly on Ge (001) for high-k dielectric applications

Description

The current work explores the crystalline perovskite oxide, strontium hafnate, as a potential high-k gate dielectric for Ge-based transistors. SrHfO3 (SHO) is grown directly on Ge by atomic layer deposition

The current work explores the crystalline perovskite oxide, strontium hafnate, as a potential high-k gate dielectric for Ge-based transistors. SrHfO3 (SHO) is grown directly on Ge by atomic layer deposition and becomes crystalline with epitaxial registry after post-deposition vacuum annealing at ∼700 °C for 5 min. The 2 × 1 reconstructed, clean Ge (001) surface is a necessary template to achieve crystalline films upon annealing. The SHO films exhibit excellent crystallinity, as shown by x-ray diffraction and transmission electron microscopy. The SHO films have favorable electronic properties for consideration as a high-k gate dielectric on Ge, with satisfactory band offsets (>2 eV), low leakage current (<10[superscript −5] A/cm[superscript 2] at an applied field of 1 MV/cm) at an equivalent oxide thickness of 1 nm, and a reasonable dielectric constant (k ∼ 18). The interface trap density (Dit ) is estimated to be as low as ∼2 × 10[superscript 12] cm[superscript −2] eV[superscript −1] under the current growth and anneal conditions. Some interfacial reaction is observed between SHO and Ge at temperatures above ∼650 °C, which may contribute to increased Dit value. This study confirms the potential for crystalline oxides grown directly on Ge by atomic layer deposition for advanced electronic applications.

Contributors

Agent

Created

Date Created
  • 2015-02-07