Search

Single-crystal silicon (Si) of six monolayer thickness was epitaxially grown on epi-germanium (Ge) in the (001) orientation at substrate temperatures lower than 300 °C, followed by direct depositio...

Single-crystal europium iron garnet (EuIG) thin films epitaxially strain-grown on gadolinium gallium garnet (GGG)(100) substrates using off-axis sputtering have strain-induced perpendicular magnetic anisotropy (PMA). By varying the sputtering conditions, we have tuned the europium/iron (Eu/Fe) composition ratios in the films to tailor the film strains. The films exhibited an extremely smooth, particle-free surface with roughness as low as 0.1 nm as observed using atomic force microscopy. High-resolution x-ray diffraction analysis and reciprocal space maps showed in-plane epitaxial film growth, very smooth film/substrate interface, excellent film crystallinity with a small full width at half maximum of 0.012$^{\circ}$ in the rocking curve scans, and an in-plane compressive strain without relaxation. In addition, spherical aberration-corrected scanning transmission electron microscopy showed an atomically abrupt interface between the EuIG film and GGG. The measured squarish out-of-plane magnetization-field hysteresis loops by vibrating sample magnetometry in conjunction with the measurements from angle-dependent x-ray magnetic dichroism demonstrated the PMA in the films. We have tailored the magnetic properties of the EuIG thin films, including saturation magnetization ranging from 71.91 to 124.51 emu/c.c. (increase with the (Eu/Fe) ratios), coercive field from 27 to 157.64 Oe, and the strength of PMA field ($H_\bot$) increasing from 4.21 to 18.87 kOe with the in-plane compressive strain from -0.774 to -1.044%. We have also investigated spin transport in Pt/EuIG bi-layer structure and evaluated the real part of spin mixing conductance to be $3.48\times10^{14} {\Omega}^{-1}m^{-2}$. We demonstrated the current-induced magnetization switching with a low critical switching current density of $3.5\times10^6 A/cm^2$, showing excellent potential for low-dissipation spintronic devices., 29 pages, 9 figures, 1 table

Molecular beam epitaxy (MBE) invented for the growth of compound semiconductors in the 70’s has been successfully extended to the advanced growth of metals, oxides, oxide/semiconductor interfaces and emergent topological materials by our endeavor in the past three and half decades. In the 80’s, Kwo et al. have invented metal MBE and oxide MBE methods in pioneering spintronics and high-temperature superconducting oxide films. In driving compound semiconductors for optoelectronics, Hong et al. have produced distributed Bragg reflectors with a continuously graded composition between each constituent without shutter operation, and greatly reduced the electrical resistance; this simple method has made easy manufacture of vertical-cavity surface-emitting lasers. In the 90’s, combining (In)GaAs and oxide MBE chambers via ultra-high vacuum, Hong et al. were the first to unpin the Fermi level in oxide/GaAs, which led to the first demonstration of inversion-channel (In)GaAs metal-oxide-semiconductor (MOS) field-effect transistors (MOSFETs). Integrating MBE, atomic layer deposition (ALD), and many other functions in ultra-high vacuum, advances have been made in pushing ultimate complementary MOS (CMOS) of record-high device performances and beyond in growing emergent topological materials for spintronics. Our novel method in preserving as-grown (In)GaAs surfaces and interfaces with high-κ oxides and metals enables employing in-situ synchrotron radiation photoemission to study electronic structures in an atomic scale.

Single-crystal metastable hexagonal perovskite YAlO3 (H-YAP) films were epitaxially grown on GaAs(111)A by utilizing sub-nanolaminated (snl) and nanolaminated (nl) atomic layer deposited (ALD) Y2O3/Al2O3 multilayers in situ on freshly prepared pristine molecular beam epitaxy (MBE) GaAs. We have studied and compared the structures of H-YAP between the snl-ALD and nl-ALD samples using synchrotron radiation X-ray diffraction (SR-XRD) and scanning transmission electron microscopy (STEM). The evolution of SR-XRD data under different annealing conditions suggested the lowest temperature of 900 °C for forming H-YAP. The observation of pronounced Pendellosung fringes indicated an excellent crystallinity of H-YAP and sharp H-YAP/GaAs interface despite an ∼8.4% large lattice mismatch between H-YAP and GaAs. Narrow full width at half-maximum (fwhm) ≈ 0.019° of H-YAP(0004) θ-rocking scan of the snl-ALD sample is close to that of substrate GaAs(111) ≈ 0.013° and 1 order of magnitude smaller than that of H-YAP(0004) of...

The role of an atomic-layer thick periodic Y&ndash, O array in inducing the epitaxial growth of single-crystal hexagonal YAlO3 perovskite (H-YAP) films was studied using high-angle annular dark-field and annular bright-field scanning transmission electron microscopy in conjunction with a spherical aberration-corrected probe and in situ reflection high-energy electron diffraction. We observed the Y&ndash, O array at the interface of amorphous atomic layer deposition (ALD) sub-nano-laminated (snl) Al2O3/Y2O3 multilayers and GaAs(111)A, with the first film deposition being three cycles of ALD-Y2O3. This thin array was a seed layer for growing the H-YAP from the ALD snl multilayers with 900 &deg, C rapid thermal annealing (RTA). The annealed film only contained H-YAP with an excellent crystallinity and an atomically sharp interface with the substrate. The initial Y&ndash, O array became the bottom layer of H-YAP, bonding with Ga, the top layer of GaAs. Using a similar ALD snl multilayer, but with the first film deposition of three ALD-Al2O3 cycles, there was no observation of a periodic atomic array at the interface. RTA of the sample to 900 &deg, C resulted in a non-uniform film, mixing amorphous regions and island-like H-YAP domains. The results indicate that the epitaxial H-YAP was induced from the atomic-layer thick periodic Y&ndash, O array, rather than from GaAs(111)A.

We report our study about the growth and characterization of $\mathrm{B}{\mathrm{i}}_{2}\mathrm{T}{\mathrm{e}}_{3}$ thin films on top of ${\mathrm{Y}}_{3}\mathrm{F}{\mathrm{e}}_{5}{\mathrm{O}}_{12}$(111), $\mathrm{T}{\mathrm{m}}_{3}\mathrm{F}{\mathrm{e}}_{5}{\mathrm{O}}_{12}$(111), $\mathrm{F}{\mathrm{e}}_{3}{\mathrm{O}}_{4}$(111), and $\mathrm{F}{\mathrm{e}}_{3}{\mathrm{O}}_{4}$(100) single-crystal substrates. Using molecular-beam epitaxy, we were able to prepare the topological insulator/ferromagnetic insulator heterostructures with no or minimal chemical reaction at the interface. We observed the anomalous Hall effect on these heterostructures and also a suppression of the weak antilocalization in the magnetoresistance, indicating a topological surface-state gap opening induced by the magnetic proximity effect. However, we did not observe any obvious x-ray magnetic circular dichroism (XMCD) on the Te ${M}_{45}$ edges. The results suggest that the ferromagnetism induced by the magnetic proximity effect via van der Waals bonding in $\mathrm{B}{\mathrm{i}}_{2}\mathrm{T}{\mathrm{e}}_{3}$ is too weak to be detected by XMCD, but still can be observed by electrical transport measurements. This is in fact not inconsistent with reported density-functional calculations on the size of the gap opening.

We have demonstrated a record low 85 mV dec−1 subthreshold slope (SS) at 300 K among the planar inversion-channel InGaAs metal-oxide-semiconductor field-effect transistors (MOSFETs). Our MOSFETs using in situ deposited Al2O3/Y2O3 as a gate dielectric were fabricated with a self-aligned inversion-channel gate-first process. The temperature-dependent transfer characteristics showed a linear reduction of SS versus temperature, with the attainment of an SS of 22 mV dec−1 at 77 K; the value is comparable to that of the state-of-the-art InGaAs FinFET. The slope factor of SS with temperature (m) is 1.33, which is lower than those reported in the planar InGaAs MOSFETs.

Y2O3 was in situ deposited on a freshly grown molecular beam epitaxy GaAs(001)-4 × 6 surface by atomic layer deposition (ALD). In situ synchrotron radiation photoemission was used to study the mechanism of the tris(ethylcyclopentadienyl)yttrium [Y(CpEt)3] and H2O process. The exponential attenuation of Ga 3d photoelectrons confirmed the laminar growth of ALD-Y2O3. In the embryo stage of the first ALD half-cycle with only Y(CpEt)3, the precursors reside on the faulted As atoms and undergo a charge transfer to the bonded As atoms. The subsequent ALD half-cycle of H2O molecules removes the bonded As atoms, and the oxygen atoms bond with the underneath Ga atoms. The product of a line of Ga–O–Y bonds stabilizes the Y2O3 films on the GaAs substrate. The resulting coordinatively unsaturated Y–O pairs of Y2O3 open the next ALD series. The absence of Ga2O3, As2O3, and As2O5 states may play an important role in the attainment of low interfacial trap densities (Dit) of

This study used high-resolution synchrotron radiation photoemission to investigate the epi SiGe(0 0 1)-2 × 1 surface that was exposed to atomic oxygen and hydrogen at room temperature, followed by in situ annealing at 500 °C. The SiGe(0 0 1)-2 × 1 surface that was grown by molecular beam epitaxy (MBE) was terminated with buckled Ge–Ge dimers, where the Ge dimers exhibited great similarity compared to those on epi Ge(0 0 1)-2 × 1. The exposure of atomic oxygen started from as low as 0.1 L up to 500 L, although the interfacial reaction practically stopped at 10 L of exposure. Atomic oxygen bonded only with the up-dimer atoms, while the atomic hydrogen passivated both dimerized atoms. Upon annealing, the GeOx oxides and GeHx hydrides disappeared completely, and the Ge region became similar to that of the clean surface. However, over half of the Ge–Ge dimers were removed from the surface after annealing in both interfaces. Heat caused the oxygen atoms in GeOx to move over to the Si region, thereby giving rise to 1+ to 4+ charge states of SiOx, which was similar to the case of the oxidation of c-Si(0 0 1)-2 × 1. The catalytic effect of Ge decreased the elevated temperature to, at most, 500 °C.

High quality Y 2 O 3 on GaSb was achieved using both molecular beam epitaxy (MBE) and atomic layer deposition (ALD) with interfacial characteristics studied by in-situ X-ray photoelectron spectroscopy (XPS) and metal-oxide-semiconductor (MOS) electrical measurements. Ga-oxide and stoichiometric Sb-oxides were obtained in the MBE-Y 2 O 3 /GaSb and non-stoichiometric Sb 2 Ox (x 2 O 3 /GaSb according to the XPS spectra. From the capacitance-voltage (CV) measurements, MBE-Y 2 O 3 provides lower interfacial trap density (D it ) grown at elevated temperature of 200°C, while ALD-grown Y 2 O 3 shows smaller hysteresis and higher dielectric constant.

In-situ molecular beam epitaxy (MBE) Y 2 O 3 films 1–2 nm thick were epitaxially grown on GaAs(001)−4×6 reconstructed surfaces. Despite a large lattice mismatch, the hetero-structure exhibits outstanding thermal stability to 900 °C with excellent capacitance-voltage ( C-V ) characteristics. Low interfacial trap densities ( D it 's ) of (3–5)×10 11 eV −1 cm −2 were obtained using the conductance method ( G-V ) without discernible peaks at the mid-gap. The frequency dispersion of the measured C-V s of the Y 2 O 3 /GaAs(001) is ~4.6% for p -GaAs and ~12.4% for n -GaAs. In contrast, the atomic layer deposited Al 2 O 3 on GaAs(001) shows large D it with a peak at the mid-gap, large C-V frequency dispersion, and low thermal stability at temperatures higher than 600 °C. Synchrotron radiation photoemission results show intactness of the interfacial structure in the MBE-Y 2 O 3 /GaAs, while removal of the surface As atoms is found in the ALD-Al 2 O 3 /GaAs system.

Molecular-beam-epitaxy (MBE) and atomic-layer-deposition (ALD) high-κ HfO 2 dielectrics have been in - situ deposited on MBE-grown pristine p - and n -In 0.53 Ga 0.47 As(0 0 1). The HfO 2 /In 0.53 Ga 0.47 As metal-oxide-semiconductor capacitors (MOSCAPs) from both methods all exhibit excellent capacitance-voltage ( C - V ) characteristics with true inversion and low leakage current densities. Moreover, interfacial trap densities ( D it ’s) with no discernible peaks at the mid-gap were measured using the temperature-dependent conductance method. Both HfO 2 /InGaAs hetero-structures have exhibited outstanding thermal stabilities to 800 °C.

Y2O3 and Al2O3 were in-situ atomic layer deposited (ALD) on pristine GaAs(001)-46 reconstructed surfaces without surface pretreatments. We have studied the border and interfacial traps in both hetero-structures using the measured electrical responses. On the basis of frequency dispersion analysis of the capacitance-voltage (CV) characteristics, we conclude that Y2O3 has effectively passivated GaAs surface with a much lower interfacial trap density (Dit) than Al2O3 as the gate dielectric. The quasi-static CV and conductance measurements are in agreement with the above conclusion. We have demonstrated an excellent ALD-Y2O3/GaAs interface with low Dit's of (0.52)1012eV1cm2 through the whole GaAs band gap without a mid-gap peak feature. Display Omitted

Molecular beam epitaxy (MBE) HfO2 films ~ 1.5 nm thick were directly deposited on freshly grown GaAs(001)-4 × 6 reconstructed surfaces. The hetero-structure exhibits outstanding thermal stability up to 900 °C with excellent capacitance-voltage (C-V) and leakage current density-electric field (J-E) characteristics. We have extracted low interfacial trap densities (Dit's) with minimum value of 1.3 × 1011 eV− 1 cm− 2 from the measured quasi-static C-V (QSCV) characteristics. The smallest frequency dispersion of the C-Vs for the MBE-HfO2/p-GaAs(001) is ~ 5.2% at frequency range of 500 to 1 MHz and no trap-induced humps were observed in the C-Vs, as measured at 100 °C and 150 °C. Also, the leakage current density remains low of 10− 8(A/cm2) at E

In-situ atomic layer deposition (ALD) Y2O3/Al2O3 in bi-layered and sub-nano-laminated structures were stacked on pristine GaAs(001) substrates for fabricating metal-oxide-semiconductor capacitors. The bi-layered Y2O3/Al2O3 showed an enhanced effective dielectric constant from 11.1 to 15.6 in capacitance-voltage characteristics with post deposition annealing to 900C. No new oxide phase formed as carefully examined using synchrotron radiation X-ray diffraction and cross-sectional high-resolution scanning tunneling electron microscopy. We designed and grew sub-nano-laminated Y2O3/Al2O3 multi-layers to simulate the mixing of gate oxides, and observed an enhanced dielectric constant of 14.8 for the as-deposited sample. Both high-temperature mixed and sub-nano-laminated ALD Y2O3/Al2O3 exhibit high dielectric constant, low leakage current ~108A/cm2 and low interfacial trap density with GaAs(001), promising for high applications in future GaAs metal-oxide-semiconductor devices. Display Omitted High dielectric constant () in 900C annealed ALD Y2O3/Al2O3 bi-layerHigh in ALD sub-nano-laminated (super-cycled) Y2O3/Al2O3 multi-layersEnhancement of dielectric constant without new structure formationExcellent CVs with low leakage current for Y2O3/Al2O3 on GaAs(001)

The Interface of Ag with p -type α2 GaAs(001)-2 × 4 has been studied to further understand the formation mechanism of the Schottky barrier height (SBH). In the initial phase of Ag deposition, high-resolution core-level data show that Ag adatoms effectively passivate the surface As-As dimers without breaking them apart. The Ag(+)-As(−) dipoles are thus generated with a maximal potential energy of 0.26 eV; a SBH of 0.38 eV was measured. Greater Ag coverage causes elemental segregation of As/Ga atoms, reversing the direction of the net dipole. The band bending effect near the interface shows a downward shift of 0.08 eV, and the final SBH is similar to the value as measured at the initial Ag deposition. Both parameters are secured at 0.25 A of Ag thickness prior to the observation of metallic behavior of Ag. Inadequacy of the metal-induced gap-state model for explaining SBH is evident.

In this paper, we investigate the embryonic stage of oxidation of an epi Ge(001)-2 &times, 1 by atomic oxygen and molecular O2 via synchrotron radiation photoemission. The topmost buckled surface with the up- and down-dimer atoms, and the first subsurface layer behaves distinctly from the bulk by exhibiting surface core-level shifts in the Ge 3d core-level spectrum. The O2 molecules become dissociated upon reaching the epi Ge(001)-2 &times, 1 surface. One of the O atoms removes the up-dimer atom and the other bonds with the underneath Ge atom in the subsurface layer. Atomic oxygen preferentially adsorbed on the epi Ge(001)-2 &times, 1 in between the up-dimer atoms and the underneath subsurface atoms, without affecting the down-dimer atoms. The electronic environment of the O-affiliated Ge up-dimer atoms becomes similar to that of the down-dimer atoms. They both exhibit an enrichment in charge, where the subsurface of the Ge layer is maintained in a charge-deficient state. The dipole moment that was originally generated in the buckled reconstruction no longer exists, thereby resulting in a decrease in the ionization potential. The down-dimer Ge atoms and the back-bonded subsurface atoms remain inert to atomic O and molecular O2, which might account for the low reliability in the Ge-related metal-oxide-semiconductor (MOS) devices.

Oxide defects in HfO 2 and Y 2 O 3 on GaAs(001) are characterized by analyzing capacitance-voltage $(C-V)$ hysteresis of metal-oxide-semiconductor capacitor (MOSCAP) under positive and negative stress fields. The $C-Vs$ of Y 2 O 3 /GaAs have smaller hysteresis and flat-band voltage shift in both accumulation and depletion regimes. This indicates less shallow and deep traps for Y 2 O 3 , making this high-k oxide more suitable than HfO 2 for GaAs passivation in terms of reliability.

By in situ depositing Y2O3 on a pristine p-In0.53Ga0.47As surface under ultra-high vacuum, we have attained a low interfacial trap density (Dit) of (2–5) × 1011 eV−1cm−2 from the mid-gap to the valence band edge. The Dit values were extracted from the conductance contours measured from 300 K to 77 K. The small frequency dispersions of 1.2%/dec (300 K) and 0.28%/dec (77 K) in the accumulation region of the capacitance–voltage (CV) characteristics and very small frequency-dependent flatband voltage shifts of 0.021 V/dec (300 K) and 0.011 V/dec (77 K) indicate low border trap densities and low Dit's; these experimental results have not been achieved in previous reports of oxide/p-In0.53Ga0.47As. The Y2O3/p-In0.53Ga0.47As heterostructure also exhibited a high thermal stability of 800 °C, as observed by the low Dit values, small CV frequency dispersions, and an abrupt interface without inter-diffusion in cross-sectional scanning transmission electron microscopy images. Our work has demonstrated a long-sought remedy for the effective passivation of p-type In0.53Ga0.47As, paving the way to high-performance electronic and optoelectronic In0.53Ga0.47As devices.

The physical investigation of surfaces and their properties crucially depends on their quality. Such investigations are commonly performed in an ultra-high vacuum environment. Thereby, the transfer of samples among different setups and under ambient conditions is desirable. The usage of a capping layer for the protection of surfaces against contaminations during long-time storage and transfer, and the subsequent temperature-controlled decapping is an established approach. However, a residual-free removal of the capping layer may present a challenge. Here, we systematically investigate the decapping process of a tellurium protected topological insulator Bi2Te3. We give evidence for the material segregation from the contaminated capping layer surface to the substrates. Therefore, a simple, temperature controlled decapping is not sufficient. We demonstrate that near perfect surfaces can be reliably obtained even after long-time storage through a combination of an initial argon ion sputtering process and a following heating for decapping. This approach is suitable for dedicated analysis systems as well as for industrial applications, large throughput of samples of arbitrary shapes, and is easily implemented in existing setups.

We performed direct microwave power injection into Pt/YIG, a heavy metal/ferrimagnetic insulator bilayer structure. The induced heating effect plays an important role in the interpretation of the ferromagnetic resonance signal. According to our frequency dependent measurements, we found the heat-induced inhomogeneous broadening in addition to the spin Hall magnetoresistance (SMR). From the angular dependent measurement, the thermal signals both in non-resonant and resonant states were observed, consistent with the angular dependence of longitudinal spin Seebeck signal. The heating effect from the injected rf power not only gives rise to the increase of inhomogeneous broadening factor ΔH 0, but also contributes to the increase of damping constant, Δα.

Transport signatures of exchange gap opening because of magnetic proximity effect (MPE) are reported for bilayer structures of Bi2Se3 thin films on yttrium iron garnet (YIG) and thulium iron garnet (TmIG) of perpendicular magnetic anisotropy (PMA). Pronounced negative magnetoresistance (MR) was detected, and attributed to an emergent weak localization (WL) effect superimposing on a weak antilocalization (WAL). Thickness-dependent study shows that the WL originates from the time-reversal-symmetry breaking of topological surface states by interfacial exchange coupling. The weight of WL declined when the interfacial magnetization was aligned toward the in-plane direction, which is understood as the effect of tuning the exchange gap size by varying the perpendicular magnetization component. Importantly, magnetotransport study revealed anomalous Hall effect (AHE) of square loops and anisotropic magnetoresistance (AMR) characteristic, typifying a ferromagnetic conductor in Bi2Se3/TmIG, and the presence of an interfacial ferromagnetism driven by MPE. Coexistence of MPE-induced ferromagnetism and the finite exchange gap provides an opportunity of realizing zero magnetic-field dissipation-less transport in topological insulator/ferromagnetic insulator heterostructures., 31 pages, 9 figures

The in-situ deposited high κ gate dielectrics, Ga 2 O 3 (Gd 2 O 3 )[GGO], Y 2 O 3 , HfO 2 , and Al 2 O 3 , on freshly molecular beam epitaxy (MBE) grown In 0.53 Ga 0.47 As (InGaAs) have perfected the interfacial electronic (chemical) characteristics, thus achieving low interfacial trap densities (D it ) and high-temperature thermal stability. These enable fabrication of self-aligned inversion- channel InGaAs metal-oxide-semiconductor field-effect- transistors (MOSFETs) using a CMOS compatible process, giving very high drain currents (I d ) of 1.05-1.8 mA/μm and transconductances (G m ) of 0.714-0.98 mS/μm in 1μm gate length (L g ) devices; Synchrotron radiation photoemission spectroscopy (SRPES) reveals no AsO x residue at the in-situ atomic layer deposited (ALD)-Al 2 O 3 /InGaAs interface, while some AsO x remains using the ex-situ method. The in-situ 1μm L g GGO/Ge pMOSFETs have given I d of 0.496 mA/μm, G m of 0.178 mS/ μm, and effective hole mobility of 389 cm2/V s. On the formation of Schottky barrier height (SBH) of Ag/GaAs, SRPES core-level data show that Ag adatoms effectively passivate the surface As-As dimers in the initial Ag deposition. A SBH of 0.38 eV is secured at Ag 0.25 A thick prior to the formation of an Ag metal. The final SBH is similar to the measured value at the initial Ag deposition.

Thulium iron garnet (TmIG) films with perpendicular magnetic anisotropy (PMA) were grown on gadolinium gallium garnet (GGG) (111) substrates by off-axis sputtering. High-resolution synchrotron radiation X-ray diffraction studies and spherical aberration-corrected scanning transmission electron microscope (Cs-corrected STEM) images showed the excellent crystallinity of the films and their sharp interface with GGG. Damping constant of TmIG thin film was determined to be 0.0133 by frequency-dependent ferromagnetic resonance (FMR) measurements. The saturation magnetization (Ms) and the coercive field (Hc) were obtained systematically as a function of the longitudinal distance (L) between the sputtering target and the substrate. A 170% enhancement of PMA field (H⊥) was achieved by tuning the film composition to increase the tensile strain. Moreover, current-induced magnetization switching on a Pt/TmIG structure was demonstrated with an ultra-low critical current density (jc) of 2.5 × 106 A/cm2, an order of magnitude smaller than the previously reported value. We were able to tune Ms, Hc and H⊥ to obtain an ultra-low jc of switching the magnetization, showing the great potential of sputtered TmIG films for spintronics.

Harnessing the spin–momentum locking of topological surface states in conjunction with magnetic materials is the first step to realize novel topological insulator-based devices. Here, we report strong interfacial coupling in Bi2Se3/yttrium iron garnet (YIG) bilayers manifested as large interfacial in-plane magnetic anisotropy (IMA) and enhancement of damping probed by ferromagnetic resonance. The interfacial IMA and damping enhancement reaches a maximum when the Bi2Se3 film approaches its two-dimensional limit, indicating that topological surface states play an important role in the magnetization dynamics of YIG. Temperature-dependent ferromagnetic resonance of Bi2Se3/YIG reveals signatures of the magnetic proximity effect of TC as high as 180 K, an emerging low-temperature perpendicular magnetic anisotropy competing the high-temperature IMA, and an increasing exchange effective field of YIG steadily increasing toward low temperature. Our study sheds light on the effects of topological insulators on magnetization dynamics, essential for the development of topological insulator-based spintronic devices. Understanding the effects of topological insulators on magnetization dynamics of adjacent magnetic materials is essential for novel spintronic devices. Here, Fanchiang et al. report thickness dependence of interfacial in-plane magnetic anisotropy and damping enhancement in Bi2Se3/yttrium iron garnet (YIG) bilayers, indicating an important role of topological surface states in the magnetization dynamics of YIG.

Display Omitted First demonstration of single-crystal atomic layer deposited oxide on GaAs(001).Attainment of very thin single crystal ALD-Y2O3 1nm thick on GaAs(001).Thin ALD-Y2O3 film with excellent crystallinity having FWHM of ~0.033?.Lowest frequency dispersion ever achieved in the ALD-oxides on n-type GaAs(001).Thermodynamic stability at high temperatures of 900?C. In situ atomic layer deposited (ALD) Y2O3 films 1-5nm thick on GaAs(001)-4i?6 reconstructed substrates were found to be single crystalline. The epitaxial growth between the oxide films and GaAs was first observed using reflective high energy electron diffraction (RHEED) and later studied using high-resolution synchrotron radiation X-ray diffraction. The Y2O3 films are of cubic phase and have (110) as the film normal; the orientation relationship between the Y2O3 films and the GaAs substrates was determined to be Y2O3(110)001] 1 ? 1 0 ]//GaAs(001)110] 1 1 ? 0 ] . The frequency dispersion of the measured capacitance-voltage (C-V) curves of the single crystal ALD-Y2O3/GaAs(001)-4i?6 is ~7% for p-GaAs and ~14% for n-GaAs (1MHz to 100Hz), lowest ever achieved in the ALD-oxides on GaAs(001).

Display Omitted Demonstration of using Al2O3/Y2O3 as common gate stacks on InGaAs, GaSb and Ge.Record high device performance of Al2O3/Y2O3 on GaSb for p-MOSFETs.Drain current of 1.5mA/µm and transconductance of 770µS/µm on InGaAs for 1µm gate length n-MOSFETs.CMOS compatible process. Y2O3, as a common high ? gate dielectric, has been directly deposited on (In)GaAs, GaSb, and Ge using electron beam evaporation in ultra-high vacuum. These semiconductors have distinctly different chemical bonding and surface electronic characteristics. No interfacial passivation layer was employed. High-quality Y2O3/semiconductor interfaces have been achieved, resulting in low interfacial trap densities and high-temperature thermal stability, essential for the CMOS compatible process. Self-aligned inversion channel n-InGaAs, p-GaSb, and p-Ge MOSFETs have been fabricated with excellent device performances.

Harnessing the spin–momentum locking of topological surface states in conjunction with magnetic materials is the first step to realize novel topological insulator-based devices. Here, we report strong interfacial coupling in Bi2Se3/yttrium iron garnet (YIG) bilayers manifested as large interfacial in-plane magnetic anisotropy (IMA) and enhancement of damping probed by ferromagnetic resonance. The interfacial IMA and damping enhancement reaches a maximum when the Bi2Se3 film approaches its two-dimensional limit, indicating that topological surface states play an important role in the magnetization dynamics of YIG. Temperature-dependent ferromagnetic resonance of Bi2Se3/YIG reveals signatures of the magnetic proximity effect of TC as high as 180 K, an emerging low-temperature perpendicular magnetic anisotropy competing the high-temperature IMA, and an increasing exchange effective field of YIG steadily increasing toward low temperature. Our study sheds light on the effects of topological insulators on magnetization dynamics, essential for the development of topological insulator-based spintronic devices., Understanding the effects of topological insulators on magnetization dynamics of adjacent magnetic materials is essential for novel spintronic devices. Here, Fanchiang et al. report thickness dependence of interfacial in-plane magnetic anisotropy and damping enhancement in Bi2Se3/yttrium iron garnet (YIG) bilayers, indicating an important role of topological surface states in the magnetization dynamics of YIG.

The integration of quantum materials like topological insulators (TIs) with magnetic insulators (MIs) has important technological implications for spintronics and quantum computing. Here we report excellent crystallinity of c-axis oriented epitaxial TI films Bi2Se3 grown on MI films, a rare earth iron garnet (ReIG), such as thulium iron garnet (Tm3Fe5O12, TmIG) by molecular beam epitaxy (MBE) with a Se-buffered low-temperature (SBLT) growth technique. We demonstrated a streaky reflection high-energy electron diffraction pattern starting from the very first quintuple layer of Bi2Se3, indicating the high-quality interface between TmIG and Bi2Se3, a prerequisite for studying interfacial exchange coupling effects. The strong interfacial exchange interaction was manifested by observations of anomalous Hall effect in the Bi2Se3/TmIG bilayer and a shift of ferromagnetic resonance field of TmIG induced by Bi2Se3. We have reproducibly grown high-quality Bi2Se3/ReIG and interfaces using this new TI growth method, which may be applied to grow other types of van der Waals (vdW) hetero-structures., Comment: 17 pages, 4 figures

The surface As/Ga atoms 3d core-level spectra of the atomically clean GaAs(1 1 1)A-2 × 2, GaAs(0 0 1)-2 × 4, and GaAs(0 0 1)-4 × 6 surfaces were firstly presented using high-resolution synchrotron radiation photoemission as a probe. The technique clearly explicates behaviors of the As atoms in different surface reconstruction. For GaAs(1 1 1)A-2 × 2, the surface As sits in the same plane as the Ga atoms. As to the GaAs(0 0 1)-2 × 4 surface, the As–As dimers dominate the surface layer, while for GaAs(001)-4 × 6, the As existed in two forms, the As in the As–Ga dimer and the 3-fold coordinated As. Next, we present a microscopic view of in situ atomic layer deposition (ALD) of Al2O3 on GaAs taking the two (0 0 1) surfaces as examples. The precursors were trimethylaluminum (TMA) and water. TMA could exist in either a chemisorbed or physisorbed form, depending on the charge environment of the associated surface atoms. The subsequent water purge resulted in both adsorbed forms being etched off or transformed the physisorbed TMA into the As-O-Al(CH3)2 configuration. We found that the ALD process rendered the precursors partially and selectively in forming bonds with the surface atoms without disturbing the atoms in the subsurface layer. Upon annealing, the interfacial bonding was dominated with the As Al as well as Ga O bonds.

Ga"2O"3(Gd"2O"3) [GGO] 3.5nm-thick, with an in situ Al"2O"3 cap 1.5nm thick, has been directly deposited on Ge substrate without employing interfacial passivation layers. The equivalent oxide thickness (EOT) of the gate stack is 1.38-nm. The metal-oxide-semiconductor (MOS) capacitors using Al"2O"3/GGO as the gate dielectric have given capacitance-voltage characteristics with frequency dispersions of ~4% at accumulation (10kHz-1MHz) and frequency dependent flat-band voltage shift (~30mV). The dielectric constant of the GGO remains at 14-15. Furthermore, the TiN/Al"2O"3/GGO/Ge pMOSFET with a gate length of [email protected] has given a saturation drain current density, a maximum transconductance and a field-effect hole mobility of [email protected]/@mm, [email protected]/@mm, and 300cm^2/Vs, respectively.

The integration of higher carrier mobility materials to increase drive current capability in the next CMOS generations is required for device scaling. But a fundamental issue regarding the introduction of high-mobility III–V in CMOS is the electrical passivation of the interface with the high-κ gate dielectric. In this work, we show that in situ H2S surface treatment on GaAs(001) leads to a stable and reorganized oxide/III–V interface. The exposition of the GaAs surface is monitored in situ by RHEED and the interface is characterized by XPS analyses. Finally, MOS capacitors are fabricated to extract interface state density over the band gap. These results highlight a promising re-interest in chalcogenide passivation of III–V surfaces for CMOS applications.

Al"2O"3, HfO"2, and composite HfO"2/Al"2O"3 films were deposited on n-type GaN using atomic layer deposition (ALD). The interfacial layer of GaON and HfON was observed between HfO"2 and GaN, whereas the absence of an interfacial layer at Al"2O"3/GaN was confirmed using X-ray photoelectron spectroscopy and transmission electron microscopy. The dielectric constants of Al"2O"3, HfO"2, and composite HfO"2/Al"2O"3 calculated from the C-V measurement are 9, 16.5, and 13.8, respectively. The Al"2O"3 employed as a template in the composite structure has suppressed the interfacial layer formation during the subsequent ALD-HfO"2 and effectively reduced the gate leakage current. While the dielectric constant of the composite HfO"2/Al"2O"3 film is lower than that of HfO"2, the composite structure provides sharp oxide/GaN interface without interfacial layer, leading to better electrical properties.

This work presents the in situ reflection high-energy electron diffraction (RHEED), scanning tunneling microscopy (STM) and synchrotron-radiation photoemission studies for the morphological and interfacial chemical characterization of in situ atomic layer deposited (ALD) Al"2O"3 on pristine molecular beam epitaxy (MBE) grown Ga-rich n-GaAs (100)-4x6 surface. Both the RHEED pattern and STM image demonstrated that the first cycle of ALD-Al"2O"3 process reacted immediately with the GaAs surface. As revealed by in situ synchrotron-radiation photoemission studies, two types of surface As atoms that have excess in charge in the clean surface served as reaction sites with TMA. Two oxidized states were then induced in the As 3d core-level spectra with chemical shifts of +660meV and +1.03eV, respectively.

High-quality (0001)-oriented ZnO epitaxial films have been grown by pulsed laser deposition on Si(111) buffered with a nanometer-thick Gd2O3(Ga2O3), GGO, layer. The structural characteristics of the ZnO epi-layers were studied by X-ray diffraction and transmission electron microscopy (TEM). The in-plane epitaxial relationship between the wurtzite ZnO, cubic GGO, and cubic Si follows {1010}ZnO∥{422}Gd2O3∥{422}Si and the ZnO/GGO interface can be described by the domain matching epitaxy. TEM contrast analysis reveals that the major defect structures in the ZnO films are edge-type threading dislocations and intrinsic basal plane stacking faults. All the ZnO epi-films studied are under a tensile biaxial strain, but no cracks were found. Temperature-dependent photoluminescence results show the excellent optical properties of the obtained ZnO layers, and the origins of the spectral features are discussed.

Nanometer-thick Y 2 O 3 films were grown epitaxially on GaN (0 0 0 1) using molecular beam epitaxy (MBE). The structures of the oxide films were studied in situ by reflection high energy electron diffraction (RHEED) during the growth and ex situ by high resolution X-ray diffraction using synchrotron radiation. At atmospheric pressure, Y 2 O 3 exists in either cubic or hexagonal structure. For the first time, the high-pressure monoclinic phase of Y 2 O 3 , stabilized by epitaxy, was prepared and preserved under atmospheric pressure. The electrical characterization carried out on the Y 2 O 3 /GaN metal-oxide-semiconductor (MOS) capacitors showed a leakage current density of ∼3.3×10 −6 A/cm 2 at 1.5 MV/cm, which remained almost the same after 800 °C annealing. A dielectric constant of ∼20 and a hysteresis of ∼250 mV were deduced from the capacitance–voltage ( C – V ) curves for the epitaxial monoclinic Y 2 O 3 .

Achievement of low interfacial densities of states, small equivalent oxide thickness, high κ values, and thermal stability at high temperatures in the high κ dielectrics on high carrier mobility semiconductors, the leading candidates for technology beyond Si CMOS, has been made using MBE. This paper reviews our recent advances in meeting the unprecedented demands in materials and physics for the new technology. Moreover, self-aligned inversion-channel InGaAs and Ge MOSFETs using MBE-Ga 2 O 3 (Gd 2 O 3 ) as the gate dielectric are compared favorably with those using the gate dielectrics made from other thin film techniques.