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Single-crystal hexagonal perovskite YAlO3 has been attained through postdeposition rapid thermal annealing with temperatures above 900 °C on nanolaminated atomic-layer-deposited Y2O3 (2.03 nm)/Al2O3 (1.08 nm) multilayers. The perovskite film is epitaxially grown on GaAs(111)A substrates. The crystallography of the heterostructure was studied utilizing synchrotron radiation x-ray diffraction (XRD) and scanning transmission electron microscopy (STEM). The epitaxial relationship between YAlO3 and GaAs is YAlO3 ( 0001 ) [ 11 2 ¯ 0 ] ∥ GaAs ( 111 ) [ 10 1 ¯ ], as determined from the radial scan along the in-plane direction. The cross-sectional STEM image reveals that the crystalline YAlO3 is continuous and the XRD study detects no other crystalline phases.

InAs MOS devices passivated with molecular beam epitaxy (MBE)-grown Gd2O3 2–3 monolayers thick followed by an Al2O3 cap have demonstrated excellent electrical performances and interfacial properties. Band offset energies of in situ atomic-layer-deposited (ALD)-Al2O3/MBE-Gd2O3/InAs and ALD-Al2O3/InAs were determined by in situ x-ray photoelectron spectroscopy in conjunction with Fowler–Nordheim tunneling current analysis. A conduction-band offset energy (ΔEc) and a valence-band offset energy of 2.3 and 3.92 eV for ALD-Al2O3/InAs were determined, respectively. The insertion of a Gd2O3 layer increases the value of ΔEc by nearly 0.1 eV as compared to the case for Al2O3 directly deposited on InAs. The distribution of interfacial density of states (Dit) within the InAs bandgap, deduced by the conductance method at 77 K, gives a low Dit value of 1012 cm−2 eV−1 near the conduction-band edge. Moreover, with energy band engineering in the heterostructure, gate-first depletion channel InAs MOSFETs have produced drai...

Self-aligned inversion-channel In0.2Ga0.8As metal-oxide-semiconductor field-effect transistors (MOSFETs) with in situ molecular beam epitaxy grown Al2O3/Ga2O3(Gd2O3) (GGO) as a gate dielectric and a TiN metal gate have been fabricated on GaAs (100) substrates. A 4 μm gate-length MOSFET using a gate dielectric of Al2O3 (3 nm thick)/GGO (8 nm thick) demonstrates a maximum drain current of 9.5 μA/μm and an extrinsic transconductance of 3.9 μS/μm. The device performances are compared favorably with those of other inversion-channel GaAs MOSFETs on GaAs (100) and also of the device on GaAs (111)A substrates using atomic layer deposited Al2O3 as a gate dielectric.

The strain/relaxation behavior of nanometer thick Y2O3 (111) epitaxially grown on Si (111) has been investigated with x-ray diffraction using synchrotron radiation. The authors systematically measured a series of Bragg reflections to determine the lattice parameters of Y2O3 films with thickness ranging from 1.6 to 9.5 nm. The strain state of the oxide lattice along surface normal and lateral directions is analyzed as a function of the oxide thickness. The spectra of Si 2p and Y 3d, obtained with in situ angle-resolved x-ray photoelectron spectroscopy on Y2O3 5 nm thick, showed no Y silicide but a very small incorporation of Si into the Y2O3 films at the interface.

The metal-oxide-semiconductor (MOS) capacitors of Al2O3∕Ga2O3(Gd2O3) on n- and p-type In0.2Ga0.8As with different metal gates exhibited excellent capacitance-voltage (C-V) characteristics and remarkable thermodynamic stability after rapid thermal annealing up to 850°C. The flat-band voltage (Vfb), flat-band voltage shift (ΔVfb), threshold voltage (Vth), and frequency dispersion of the MOS capacitors with different metal gates were extracted from the C-V curves. The Vth values of Al2O3∕Ga2O3(Gd2O3)∕p-In0.2Ga0.8As were calculated to be about 0.04V (Al gate) and 1.15V (Ni gate) and those of Al2O3∕Ga2O3(Gd2O3)∕n-In0.2Ga0.8As −1.94V (Al gate) and −0.88V (Ni gate). The correlation between flat-band voltage and different metal gates indicates unpinned Fermi levels at the metal/dielectric interfaces.

High-κ dielectric Ga2O3(Gd2O3) (GGO) has been deposited on Ge (100) at room temperature using molecular beam epitaxy. In situ angular-resolved x-ray photoelectron spectroscopy on the GGO/Ge after gate dielectric deposition and 500°C postdeposition annealing has exhibited negligible Ge interdiffusion, thus revealing high thermal stability of the heterostructure. The CF4-plasma treatment on the passivated GGO/Ge has greatly improved the capacitance-voltage characteristics of the metal-oxide-semiconductor capacitors, besides the very low gate leakage current density of 3.2×10−9A∕cm2 at a flat-band voltage +1V. These excellent interfacial characteristics have been achieved without employing any intentional passivation layers.

dc and rf characteristics of self-aligned inversion-channel In0.53Ga0.47As metal-oxide-semiconductor field-effect transistors (MOSFETs) using molecular beam epitaxy (MBE) deposited Al2O3/Ga2O3(Gd2O3) (GGO) high κ dielectrics and TiN metal gates are reported. MOSFETs with various oxide thicknesses were fabricated. The In0.53Ga0.47As MOSFETs using Al2O3(2 nm)/GGO (5 nm) gate dielectric demonstrated a maximum drain current of 1.05 mA/μm and a peak transconductance of 714 μS/μm, both are the highest values ever reported for enhancement-mode InGaAs MOSFETs with 1 μm gate length. In addition, the same transistors exhibited excellent embedded rf properties and achieved a fT of 17.9 GHz and a fmax of 12.1 GHz. The high-quality in situ MBE growth of high κ dielectrics/InGaAs has attributed to the high device performance.

High-quality single-crystal nanothick Y2O3 films have been grown epitaxially on Si (111) despite a lattice mismatch of 2.4%. The films were electron beam evaporated from pure compacted powder Y2O3 target in ultrahigh vacuum. Y2O3 3nm thick exhibited a bright, sharp, streaky reconstructed (4×4) reflection high energy electron diffraction pattern. Structural studies carried out by x-ray diffraction with synchrotron radiation and high-resolution transmission electron microscopy show that the films have the cubic bixbyite phase with a remarkably uniform thickness and high structural perfection. Two Y2O3 domains of B-type Y2O3[21¯1¯]∥Si[112¯] and A-type Y2O3[21¯1¯]∥Si[21¯1¯] coexist in the initial film growth with B type predominating over A type in thicker films as studied using x-ray diffraction. The narrow full width at half maximum of 0.014° in the ω-rocking curve is the characteristic of excellent crystalline films. High-resolution transmission electron microscopy and fast Fourier transform analysis show ...

Molecular beam epitaxy (MBE) was employed to grow nanothick high κ HfO2 films on Si (100) as templates to suppress the formation of the oxide/Si interfacial layer during the subsequent atomic layer deposited (ALD) HfO2 growth. A metal-oxide-semiconductor (MOS) diode with the ALD/MBE bilayer stack of an equivalent oxide thickness (EOT) of ∼1.1nm has demonstrated markedly low electrical leakage of 8.3×10−3A∕cm2 at Vfb−1V, a reduction by five order of magnitudes, comparing with those using SiO2 of the same EOT. The attainment of high dielectric constant and very small frequency dispersion in capacitance-voltage (C-V) curves suggests the absence of low κ capacitors in series near the oxide/Si interface. Furthermore, MOS field-effect transistors (MOSFETs) based on the ALD/MBE-HfO2 composites have been fabricated having excellent device performance, with a drain current (ID) of 240mA∕mm and transconductance (Gm) of 120mS∕mm. These are superior to those of the MOSFETs using either ALD (55mA∕mm, 60mS∕mm) or MBE (...

Molecular beam epitaxy deposited Ga2O3(Gd2O3) on Ge, without a commonly employed interfacial layer of GeON, has demonstrated excellent electrical properties, such as a high κ value of 14.5, a low electrical leakage current density, and well behaved C-V characteristics even being subjected to 500°C annealing in N2 ambient for 5min. In situ angle-resolved x-ray photoelectron spectroscopy (XPS) studies have revealed an abrupt Ga2O3(Gd2O3)∕Ge interface without forming any interfacial layer. Further XPS studies explained the outstanding thermodynamic stability of the Ga2O3(Gd2O3)∕Ge heterostructure.

The authors report on the growth of GaN by nitrogen plasma-assisted molecular beam epitaxy (MBE) on a 2in. Si (111) substrates with a nanothick (∼4.8nm thick) γ-Al2O3 as a template/buffer. A thin layer of MBE-AlN ∼40nm thick was inserted prior to the growth of GaN. High-resolution transmission electron microscopy (HR-TEM) and high-resolution x-ray diffraction studies indicated that both of the nanothick γ-Al2O3 and AlN are a single crystal. Reflection high-energy electron diffraction, high-resolution x-ray scattering using synchrotron radiation, and cross-sectional HR-TEM measurements indicated an orientation relationship of GaN(0002)∥AlN(0002)∥γ-Al2O3(111)∥Si(111) and GaN[10−10]∥AlN[10−10]∥γ-Al2O3[2−1−1]∥Si[2−1−1]. A dislocation density of 5×(108–109)∕cm2 in the GaN ∼0.5μm thick was determined using cross-sectional TEM images under weak-beam dark-field conditions.

The scalability of molecular beam epitaxy grown Ga2O3(Gd2O3)∕In0.2Ga0.8As∕GaAs with in situ Al2O3 capping layers has been studied, in which the InGaAs surface Fermi level has been unpinned. The electrical and structural properties were improved with rapid thermal annealing to high temperatures of 800°C under N2 flow. As Ga2O3(Gd2O3) is scaled down to 8.5nm, the dielectric constant maintained at 14–15, similar to those of thicker oxides, resulting in an equivalent oxide thickness of 2.3nm. A low gate oxide leakage current density of 10−9A∕cm2 at ∣VG−Vfb∣=1, small flatband voltage shift (ΔVfb), low interfacial density of states (Dit) of (1–3)×1011cm−2eV−1 have been achieved.

The depth profile of the HfO2∕Si interface grown by molecular beam epitaxy (MBE) has been investigated by high-resolution x-ray photoelectron spectroscopy using synchrotron radiation beam and low energy Ar+ sputtering. At the interfacial layer, the Hf 4f spectra show a Hf silicide state without a Hf silicate signal. The O 1s and Si 2p spectra show weakly two silicon oxidation states of SiO and SiO2. The data suggest an inward reaction of the Hf and O species into the Si substrate during the MBE growth. The valence band offset (ΔEV) of ∼3.5eV is obtained for the HfO2∕Si interface by measuring the valence-band edges of HfO2 and Si.

Heteroepitaxy of single-crystal Gd2O3 on GaN (with a wurtzite hexagonal close-packed (hcp) structure) and single-crystal GaN on Gd2O3 was achieved. In situ reflection high-energy electron diffraction reveals a sixfold symmetry in the in-plane epitaxy of the rare earth oxide on GaN and also in the overgrowth of GaN on the oxide. Single-crystal x-ray diffraction measurements find that these single-crystal oxide films are indeed the high temperature hexagonal phases of the sesquioxides, stabilized by the GaN substrate epitaxy. Despite a large mismatch in the lattice constant, the fully relaxed oxide films are of excellent structural quality. The x-ray diffraction results revealed that the GaN grown on the rare earth oxide is a single-crystal and has the same crystallographic hcp structure as the underlying GaN. The structures of both layers of GaN were also studied by cross section transmission electron microscopy.

A fluorite-related phase of Gd2O3, with a tetragonal unit cell of a=5.65 A and c=5.37 A, was attained in this study. The new phase was found either in a thin Gd2O3 film (∼18 A), which was epitaxially grown on GaAs(100), or in a disordered (by mild Ne+-ion sputtering) and recrystallized (by UHV annealing) thin cubic α-Gd2O3 film. The structural characteristics of the new oxide films were studied using in situ reflection high-energy electron diffraction, secondary-electron imaging, and single-crystal x-ray diffraction.

Growth of a single crystal was found in the first few oxide layers on GaAs(100) substrate, electron beam evaporated from a Ga5Gd3O12 source. Reflection high-energy electron diffraction and x-ray diffraction studies show that the thin oxide film is epitaxially grown on GaAs with the surface normal (110) and in-plane axis [001] parallel to (100) and [011] of GaAs, respectively, and the crystallographic structure is isomorphic to Mn2O3. The chemical composition of the oxide film was determined by x-ray photoelectron spectroscopy to be unequivocally pure Gd2O3. Based on Gibbs free energies of formation for all possible pairs in Ga, As, Gd, and O, a model is proposed to explain the epitaxy and the growth of single-domain Gd2O3 on GaAs.

Ga2O3(Gd2O3), electron beam evaporated from a single crystal Ga5Gd3O12 garnet, was ex situ deposited on molecular beam epitaxy grown GaN of Ga-polar surface. Using capacitance–voltage measurement, accumulation and depletion behavior was observed in the Ga2O3(Gd2O3)/GaN metal–oxide–semiconductor diodes, with an interfacial density of states less than 1011 cm−2 eV−1. The Ga2O3(Gd2O3)/GaN interface remains intact with the samples subject to rapid-thermal annealing up to 950 °C, as studied from x-ray reflectivity measurements.

The role of Gd2O3 is investigated in our previously discovered oxide films of Ga2O3(Gd2O3) for GaAs surface passivation. Based on the systematic dependence of the dielectric properties of (Ga2O3)1−x(Gd2O3)x on the Gd (x) content, we showed that pure gallium oxide does not effectively passivate GaAs, and Gd2O3 is a necessary component to stabilize the gallium oxide in the 3+ fully oxidized state due to the electropositive nature of Gd+3. This gives rise to electrically insulting films of low leakage current and high electrical breakdown strength.

We have successfully fabricated depletion mode GaAs metal–oxide–semiconductor field effect transistors using Ga2O3(Gd2O3) as the gate oxide and an oxygen implant isolation technique. Growth of the device structure including the deposition of Ga2O3(Gd2O3) was performed in a multichamber molecular beam epitaxy system. A 1 μm×100 μm device shows excellent dc and microwave characteristics with low output conductance. Complete pinchoff at Vg=−2.5 V and operation in the accumulation mode of up to Vg=2.5 V were measured. The maximum transconductance was 100 mS/mm, with a high drain current density of 315 mA/mm. Microwave testing yielded a fT of 14 GHz and a fmax of 35 GHz.

Ga2O3(Gd2O3)–GaAs heterostructures in situ fabricated using a multichamber ultrahigh vacuum (molecular beam epitaxy) system were studied by x-ray reflectivity measurement and high-resolution transmission electron microscopy. The oxide–GaAs interfaces were found to be very smooth with the roughness no more than 1 nm. Moreover, an interfacial roughness as small as one atomic layer of GaAs (0.33 nm) was observed using x-ray reflectivity.