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Single-crystal Si films six-monolayers in thickness were epitaxially grown on Ge(001) surface to minimize the formation of undesirable GeO x with subsequent deposition of HfO2 and Y2O3. The interfacial properties and reliability of the in-situ deposited high-κ oxides on epi-Si/p-Ge(001) were compared. We have achieved interface trap density (D it) values of (1–3) × 1011 eV−1cm−2 in the Y2O3/epi-Si/p-Ge(001), which are two times lower than those of the HfO2/epi-Si/p-Ge(001). The capacitance-equivalent-thicknesses under different annealing conditions were extracted to analyze the interdiffusion in the gate stacks under various thermal treatments. Y2O3/epi-Si/Ge exhibited higher thermal stability than HfO2/epi-Si/Ge. In both high-κ’s gate stacks, the effective charge sheet densities (ΔN eff) are lower than the targeted value of 3 × 1010 cm−2. Compared to the Y2O3 gate stacks, attainment of a high acceleration factor of 11 in the HfO2 gate stacks suggested an improved defect-carrier decoupling in the latter stacks.

Germanium-on-insulator (GeOI) structures with a surface orientation of (111) have been successfully fabricated by using low thermal budget epitaxial-lift-off (ELO) technology via direct bonding and selective etching. The material characteristics and transport properties of the Ge(111)OI structure have been systematically investigated through secondary-ion mass spectrometry, Raman spectroscopy, X-ray diffraction, high-resolution transmission electron microscope, and Hall measurement. The transferred Ge (111) layer remained almost intact from the as-grown epitaxial layers, indicating the benefits of ELO technology. The low thermal budget ELO technology demonstrated in this work is promising to integrate Ge channels with different surface orientations on Si (100) substrates for future monolithic 3D applications.

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.

A microscopic view of O2 adsorption on an epi Ge(001)-2 × 1 surface at room temperature, as studied by synchrotron radiation photoemission, is presented. One of the dissociated O atoms etches off the up-dimer atom to form the GeO species. The other dissociated O atom fills the vacancy and bonds with the underneath Ge atom in the subsurface layer. The down-dimer atom and its backbond with the subsurface atom remain inert to O2. The present investigation reports the notorious effect of O2 on the Ge surface, which should not be overlooked in Ge metal–oxide–semiconductor (MOS) device development.

Using in situ synchrotron-radiation photoelectron spectroscopy, the band offsets and the surface dipole potential energy for cycle-by-cycle atomic layer deposited (ALD) Y2O3 on p-type GaAs(0 0 1)-4 × 6 were studied. We have characterized the electronic property for laminar films. The valence- and conduction-band offsets and interfacial dipole potential energy are approximately 1.75, 2.4, and 0.46 eV, respectively. The dipole direction points outward, showing that Y(+) is located at the topmost layer and the O(−) ions participate in the bonding with the GaAs surface atoms.

Research efforts on achieving low interfacial density of states (Dit) as well as low electrical leakage currents on GaAs-based III–V compound semiconductors are reviewed. Emphasis is placed on ultra high vacuum (UHV) deposited Ga2O3(Gd2O3) and atomic layer deposition (ALD)-Al2O3 on GaAs and InGaAs. Ga2O3(Gd2O3), the novel oxide, which was electron-beam evaporated from a gallium-gadolinium-garnet target, has, for the first time, unpinned the Fermi level of the oxide/GaAs heterostructures. Interfacial chemical properties and band parameters of valence band offsets and conduction band offsets in the oxides/III–V heterostructures are studied and determined using X-ray photoelectron spectroscopy and electrical leakage transport measurements. The mechanism of III–V surface passivation is discussed. The mechanism of Fermi-level unpinning in ALD-Al2O3ex-situ deposited on InGaAs were studied and unveiled. Systematic heat treatments under various gases and temperatures were studied to achieve low leakage currents of 10-8–10-9 A/cm2 and low Dit's in the range of (4–9)×1010 cm-2 eV-1 for Ga2O3(Gd2O3) on InGaAs. By removing moisture from the oxide, thermodynamic stability of the Ga2O3(Gd2O3)/GaAs heterostructures was achieved with high temperature annealing, which is needed for fabricating inversion-channel metal–oxide–semiconductor filed-effect transistors (MOSFET's). The oxide remains amorphous and the interface remains intact with atomic smoothness and sharpness. Device performances of inversion-channel and depletion-mode III–V MOSFET's are reviewed, again with emphasis on the devices using Ga2O3(Gd2O3) as the gate dielectric.

Photoemission from an epi Ge(001)-2 × 1 surface is presented using synchrotron radiation as a probe. The topmost surface atoms are buckled with the up-dimer and down-dimer atoms exhibiting surface core-level shifts (SCLSs) of −0.492 and −0.178 eV, respectively. The subsurface layer shows a +0.083 eV SCLS. The final-state effect suffices to explain the sign of the shift. The electron affinity and ionization potential for the epi Ge surface are 4.36 and 5.09 eV, respectively. An argument contrasting the current results with those of existing reports with non-epi surfaces is also given. Non-epi surfaces possess Ge surfaces with isolated single atoms or small droplets that affect Ge's contact with dielectric layers and the electric performances of the Ge metal–oxide–semiconductor structure.

Unlike coherent acoustic phonons (CAPs) generated from heat induced thermal stress by the coated Au film, we demonstrated the oscillation from c-ZnO epitaxial film on oxide buffered Si through a degenerate pump–probe technique. As the excited photon energy was set below the exciton resonance, the electronic stress that resulted from defect resonance was used to induce acoustic wave. The damped oscillation revealed a superposition of a high frequency and long decay CAP signal with a backward propagating acoustic pulse which was generated by the absorption of the penetrated pump beam at the Si surface and selected by the ZnO layer as the acoustic resonator.

A low interfacial trap density (D it) of 2.2 × 1011 eV−1 cm−2 has been achieved with an atomic layer deposited (ALD) single crystal Y2O3 epitaxially on n-GaAs(001), along with a small frequency dispersion of 10.3% (2.6%/decade) at the accumulation region in the capacitance–voltage (C–V) curves. The D it and frequency dispersion in the C–V curves in this work are the lowest among all of the reported ALD-oxides on n-type GaAs(001). The D it was measured using the conductance–voltage (G–V) and quasi-static C–V (QSCV) methods. Moreover, the heterostructure was thermally stable with rapid annealing at 900 °C under various durations in He and N2, which has not been achieved in the heterostructures of ALD-Al2O3 or HfO2 on GaAs.

During the initial stage of atomic layer deposition, the exposure of a GaAs(111)A-2×2 surface to trimethylaluminum (TMA) leads to occupying a Ga-vacancy site on the surface by a chemisorbed As-bonded aluminum with the loss of all methyl ligands. The water purge disrupts physisorbed TMA and initiates the growth of Al2O3. The subsequent growth of Al2O3 does not result in the oxidation of As, Ga, or Al in the Ga vacancy. The reconstructed Ga atoms retain the bulk-terminated positions resulting in a dangling bond, and all As atoms become four-fold coordinated. The correlation of an interfacial electronic structure with an electric performance is discussed for Al2O3 on GaAs(001)-2×4 and GaAs(001)-4×6.

The electronic structure of single-crystal (In)GaAs deposited with tri-methylaluminum (TMA) and water via atomic layer deposition (ALD) is presented with high-resolution synchrotron radiation core-level photoemission and capacitance-voltage (CV) characteristics. The interaction of the precursor atoms with (In)GaAs is confined at the topmost surface layer. The Ga-vacant site on the GaAs(111)A-2 × 2 surface is filled with Al, thereby effectively passivating the As dangling bonds. The As-As dimers on the GaAs(001)-2 × 4 surface are entirely passivated by one cycle of TMA and water. The presumed layerwise deposition fails to happen in GaAs(001)-4 × 6. In In0.20Ga0.80As(001)-2 × 4, the edge row As atoms are partially bonded with the Al, and one released methyl then bonds with the In. It is suggested that the unpassivated surface and subsurface atoms cause large frequency dispersions in CV characteristics under the gate bias. We also found that the (In)GaAs surface is immune to water in ALD. However, the momentary exposure of it to air (less than one minute) introduces significant signals of native oxides. This indicates the necessity of in situ works of high κ/(In)GaAs-related experiments in order to know the precise interfacial atomic bonding and thus know the electronic characteristics. The electric CV measurements of the ALD-Al2O3 on these (In)GaAs surfaces are correlated with their electronic properties.

Y2O3 and Al2O3 were deposited onto GaSb(100) surfaces by molecular beam epitaxy and atomic layer deposition, respectively. Angle-resolved X-ray photoelectron spectroscopy and electrical measurements were used to probe the two oxide/semiconductor interfaces, which yielded very different behaviors. Highly surface-sensitive scans showed traces of SbOx and AsOx at the Y2O3 surface, which were removed during subsquent ALD Al2O3. The deposition of Y2O3 led to true inversion as indicated in capacitance–voltage (C–V) characteristics, small hysteresis and frequency dispersion, and low gate leakage. In contrast, for Al2O3/GaSb, the GaSb remained virtually intact, with Al2O3 bonding to the residual As, leading to poor C–V characteristics.

The interfacial density of states (Dit) distribution of high-κ dielectric Ga2O3(Gd2O3) [GGO] directly deposited on n-type Ge(100) without invoking any interfacial passivation layer (IPL) was established using conductance measurements and charge pumping (CP) technique. The conductance measurements yielded Dit values in the range of (1–4)×1011 cm-2 eV-1 from the mid-gap energy to the conduction band edge within the Ge band gap, which are consistent with the mean Dit value of ~2×1011 cm-2 eV-1 near the mid-gap obtained independently by the CP method. The flat Dit distribution at the conduction band edge compares favorably with those attained using IPLs such as SiO2/Si-cap and GeO2.

In-situ ultrahigh-vacuum-deposited Y2O3 2–3-monolayer-thick on freshly grown In0.53Ga0.47As with an Al2O3 cap were employed as a gate dielectric. A low interfacial density of states of (8–9)×1011 eV-1 cm-2 near the midgap has been measured using the conductance method. The strong Y2O3/InGaAs interfacial bonding, revealed using X-ray photoelectron spectroscopy, enables attainment of an atomically smooth interface with 750 °C annealing. Low subthreshold swing of 97 mV/decade, high drain current of 1.5 mA/µm, high transconductance of 0.77 mS/µm, and field-effect mobility of 2,100 cm2 V-1 s-1 were achieved in a self-aligned inversion-channel InGaAs metal–oxide–semiconductor field-effect-transistor of 1 µm gate length.

Molecular beam epitaxy grown Al2O3/Ga2O3(Gd2O3)/In0.20Ga0.80As/GaAs has been rapidly thermal annealed to 850 °C in N2. The hetero-structure remained intact, with the In0.20Ga0.80As/GaAs interface being free of misfit dislocation and In0.20Ga0.80As strained, as observed by high-resolution transmission electron microscopy and high-resolution x-ray diffraction using synchrotron radiation. Excellent capacitance–voltage characteristics as well as low electrical leakages were obtained. These structural and electrical results demonstrate that employing Ga2O3(Gd2O3) as a dielectric with an in situ Al2O3 capping layer efficiently protects strained InGaAs layers from relaxing and volatilizing during rapid thermal annealing to 850 °C, important for fabricating inversion-channel InGaAs metal–oxide–semiconductor field-effect-transistors, a candidate for beyond the 16 nm node complementary MOS technology.

High-quality ZnO epitaxial films were grown by pulsed-laser deposition on Si (1 1 1) substrates with a thin γ-Al2O3 buffer layer. The epitaxial γ-Al2O3 buffer layer consists of two (1 1 1) oriented domains rotated 60° from each other against the surface normal, which yields the in-plane epitaxial relationship or . The crystalline quality and optical properties of ZnO epi-layers were studied by x-ray diffraction and photoluminescence measurements. A clear correlation between ZnO deep-level emission (DLE) to near-band edge (NBE) emission intensity ratio and the width of the -scan across off-normal reflection was observed. The NBE linewidth also exhibits strong dependence on the width of the ZnO (0 0 2) rocking curve. These observations indicate the NBE and DLE emissions are mainly affected by the edge and screw type dislocations, respectively.