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High quality nanometer-thick Gd2O3 and Y2O3 (rare-earth oxide, R2O3) films have been epitaxially grown on GaN (0001) substrate by molecular beam epitaxy (MBE). The R2O3 epi-layers exhibit remarkable thermal stability at 1100 °C, uniformity, and highly structural perfection. Structural investigation was carried out by in situ reflection high energy electron diffraction (RHEED) and ex-situ X-ray diffraction (XRD) with synchrotron radiation. In the initial stage of epitaxial growth, the R2O3 layers have a hexagonal phase with the epitaxial relationship of R2O3 (0001)H⟨1120⟩H//GaN(0001)H⟨1120⟩H. With the increase in R2O3 film thickness, the structure of the R2O3 films changes from single domain hexagonal phase to monoclinic phase with six different rotational domains, following the R2O3 (201)M[020]M//GaN(0001)H⟨1120⟩H orientational relationship. The structural details and fingerprints of hexagonal and monoclinic phase Gd2O3 films have also been examined by using electron energy loss spectroscopy (EELS). A...

It is well known that Taiwan's IC industry is in the very leading front of the world, and production of 65 nm devices was launched in 2006. Within a few years, the need of high-k dielectrics and metal gates is eminent and truly indispensable. Professor H.L. Hwang (the author) organized 12 professors and 50 graduate students of National Tsing Hua University and Chiao Tung University, and executed this particular project, which is sponsored by the Ministry of Economic Affairs of Republic of China, and is aimed at treating efficiently this problem and transferred the critical technologies to industry in a time frame of 3 years.

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.

Ga2O3(Gd2O3), the novel oxide, which was electron-beam evaporated from a gallium- gadolinium-garnet target in UHV, has unpinned the GaAs Fermi level. 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 x 1010 cm-2V-1 for Ga2O3(Gd2O3) on InGaAs. By removing moisture from the oxide, thermodynamic stability of the Ga2O3(Gd2O3)/GaAs hetero-structures was achieved with high temperature annealing, which is needed for fabricating inversion-channel MOSFET's. The oxide remains amorphous and the interface remains intact with atomic smoothness and sharpness. The mechanism of Fermi-level unpinning and the band parameters in atomic layer deposition (ALD)-Al2O3 ex-situ deposited on InGaAs were studied and unveiled. The work of inversion- channel, depletion- mode, and power GaAs MOSFET's using Ga2O3 (Gd2O3) as the gate dielectric was briefly reviewed.

Continued scaling of microelectronic devices is demanding that alternatives to SiO2 as the gate dielectric be developed soon. This in turn has placed enormous pressure on the abilities of physical characterization techniques to address critical issues such as film and interface structure and composition, transport properties, and thermal or chemical stability. This article summarizes the strengths and capabilities of four techniques used for the materials characterization of alternative gate dielectrics: scanning transmission electron microscopy (STEM) in conjunction with electron energy-loss spectroscopy (EELS), medium-energy ion scattering (MEIS), infrared-absorption spectroscopy (IRAS), and x-ray photoelectron spectroscopy (XPS). The complementary nature of these techniques has allowed for a detailed picture of the various properties of alternative gate dielectrics, and in particular of the dielectric/silicon interface. Critical issues and features of several important alternative gate dielectrics, ZrO2, AI2O3, Y2O3, and Gd2O3, are explored in light of the well-studied SiO2/Si system.

We have employed molecular beam epitaxy (MBE) to grow high κ dielectric nano-thick films of Al 2 O 3 and HfO 2 on Si (1 0 0) as templates to suppress effectively the formation of the oxide/Si interfacial layer during the subsequent atomic layer deposition (ALD) growth for Al 2 O 3 . We show marked improvements of electrical performance of the ALD+MBE composite oxides. A first bi-layer composite of ALD Al 2 O 3 1.9 nm/MBE Al 2 O 3 1.4 nm showed a dielectric constant of 9.1 with an equivalent oxide thickness (EOT) of 1.41 nm. The interfacial trap density D it was 2.2×10 11 cm −2 eV −1 as deduced from the conductance method, with the leakage current density being 2.4×10 −2 A/cm 2 at V fb −1 V. The second bi-layer of ALD Al 2 O 3 3.0 nm/MBE HfO 2 2.0 nm showed a dielectric constant of 11.5 and an EOT of 1.7 nm. The D it was estimated to be 2×10 11 cm −2 eV −1 with the leakage being 1.1×10 −4 A/cm 2 at V fb +1 V.

High quality nanometer-thick Gd₂O₃ and Y₂O₃ (rare-earth oxide, R₂O₃) films have been epitaxially grown on GaN (0001) substrate by molecular beam epitaxy (MBE). The R₂O₃ epi-layers exhibit remarkable thermal stability at 1100 °C, uniformity, and highly structural perfection. Structural investigation was carried out by in situ reflection high energy electron diffraction (RHEED) and ex-situ X-ray diffraction (XRD) with synchrotron radiation. In the initial stage of epitaxial growth, the R₂O₃ layers have a hexagonal phase with the epitaxial relationship of R₂O₃ (0001)(H)1120(H)//GaN(0001)(H)1120(H). With the increase in R₂O₃ film thickness, the structure of the R₂O₃ films changes from single domain hexagonal phase to monoclinic phase with six different rotational domains, following the R₂O₃ (201)(M)[020](M)//GaN(0001)(H)1120(H) orientational relationship. The structural details and fingerprints of hexagonal and monoclinic phase Gd₂O₃ films have also been examined by using electron energy loss spectroscopy (EELS). Approximate 3-4 nm is the critical thickness for the structural phase transition depending on the composing rare earth element.

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.

Hexagonal-phase single-crystal Gd2 O3 is deposited on GaN in a molecular beam epitaxy system. The dielectric constant is about twice that of its cubic counterpart when deposited on InGaAs or Si. The capacitive effective thickness of 0.5 nm in hexagonal Gd2 O3 is perhaps the lowest on GaN-metal-oxide-semiconductor devices. The heterostructure is thermo dynamically stable at high temperatures and exhibits low interfacial densities of states after high-temperature annealing.

The Working Group on Women in Physics in China‐Taiwan (WGWP‐CT) was established in 1999 and has been active since then. In this brief report, we will introduce the progress of WGWP‐CT and the current status of women physicists in China‐Taipei. Based on solid data, we demonstrate a rapid development of group support.

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.

High-resolution medium energy ion scattering (MEIS) was used to investigate structure, composition and defects in amorphous and crystalline oxides, and their interface with silicon. Isotopic oxygen reactions were examined in several model high-κ systems, including Hf and Ce oxides, silicates and nitrided silicates as a function of composition, crystallinity and post-deposition annealing conditions. Our results show that for post-growth oxidation of Hf-based films there was extensive O exchange throughout the film which could be suppressed by the addition of SiO2. Under our growth conditions, there was no measurable interfacial SiO2 formation. In contrast Ce silicates exhibit rapid interface growth under similar oxygen exposures. Epitaxial SrTiO3 and Sc2O3 films grown by MBE on Si were studied in different channeling geometries. We show that diffusion of Ti and O during SrTiO3 film growth on Si (001) results in substitution of thin interfacial Sr

The ability of controlling the growth and interfaces of ultrathin dielectric films on Si and compound semiconductors by ultrahigh vacuum physical vapor deposition has led to comprehensive studies of gate stacks employing the high κ gate oxide Ga2O3(Gd2O3), and the rare earth oxides Gd2O3and Y2O3. The epitaxy and the interfaces of Gd2O3on GaAs, GaN, and Si were characterized with atomic precision, and show strong tendency to conform to the underlying substrate, thus providing insight into the fundamental mechanism for low interfacial state density and effective passivation of GaAs and GaN surfaces. These Gd2O3and Y2O3gate stacks of abrupt interfaces and controlled microstructures were employed as a model system to elucidate critical issues of materials integration in CMOS scaling.

As driven by continual aggressive demands of faster speed in channels and reducing power dissipation for CMOS beyond the 10 nm node, the consensus is to employ InGaAs semiconductors as the high carrier mobility channels integrated with high k gate dielectrics. (1) The realization of these new MOSFET’s depends critically and essentially on fine tuning of the high k/InGaAs interfaces. The interfacial perfection is needed for achieving the stringent requirement of a low interfacial trap density (D it) in the order of 1011 eV-1cm-2 or smaller, very low equivalent oxide thickness (EOT), defined as toxide(κSiO2/κoxide), of less than 0.5 nm, and excellent thermal stability at high temperatures. (2) In 1990s, the molecular beam epitaxy (MBE)-Ga2O3(Gd2O3) [GGO] (3,4) on GaAs and InGaAs enabled the demonstration of the first inversion-channel GaAs and InGaAs MOSFETs (5,6), opening up the new era of high performance III-V MOSFETs. Subsequently, atomic layer deposited ALD-Al2O3 has been employed to fabricate high performance planar InGaAs MOSFETs (7) and, more recently, the non-planar ones. (8,9) Here, our studies of (In)GaAs surfaces with various surface reconstructions, different orientations, and Indium contents, are reviewed. (10-12) Probing on the “true” surfaces and interfaces was made possible with our unique setup of in-situ transferring the freshly grown, pristine (In)GaAs surfaces (3,13) and high k/(In)GaAs interfaces to the Taiwan’s National Synchrotron Radiation Research Center for the photoemission measurements (12,13) to study the interface electronic characteristics. The electrical properties of the corresponding MOS capacitors (MOSCAPs) were measured and the interfacial trap densities (D it’s) within the band-gap of (In)GaAs were deduced. In general, the D it’s at the high k/(In)GaAs interfaces are higher than that at SiO2/Si. A well-passivated SiO2/Si interface, exhibiting a flat D it(E) distribution with low D it values, is the main reason for the highly performed Si MOSFETs. In contrast, ALD-Al2O3 on GaAs and InGaAs (of low In contents) has commonly shown a large broad peak around the mid-gap in D it(E). (14) Moreover, the CV curves of p- and n-type ALD-Al2O3/GaAs MOSCAPs have shown notable disparity in frequency dispersion.(13-16) This is the major cause for poorly performed ALD-Al2O3/GaAs (and In0.2Ga0.8As) MOSFETs, which showed very little drain currents. However, in the tailored high k/(In)GaAs interfaces, the D it has been lowered to the range of 1011 eV-1cm-2. A notable example is the MBE-GGO on In0.2Ga0.8As of both the p- and n- MOSCAPs, which have shown much less frequency dispersion in the accumulation region. (2,17) Furthermore, using metal gates of different work functions, small differences between theoretical and measured flat-band voltages (Vfb ) were demonstrated, suggesting a high degree of Fermi-level movement efficiency at the metal/Al2O3 and the GGO/p- and n-In0.2Ga0.8As interface. (17) The very different CV behaviors for MBE-GGO and ALD-Al2O3 have warranted systematic electrical measurements to obtain the D it(E) distributions, (18) as will be discussed. Self-aligned inversion-channel MBE-Al2O3/GGO/ In0.53Ga0.47As MOSFETs exhibited a maximum drain current (I D) of 1.05 mA/μm, a transconductance (G m) of 0.7 mS/μm, a peak electron mobility (μe ) of 1300 cm2/V∙s, and sub-threshold swing (SS) of 103 mV/dec (19). Extending the in-situ MBE approach to grow high-κ Y2O3 on In0.53Ga0.47As, we have achieved self-aligned inversion-channel In0.53Ga0.47As MOSFETs with better performance: an I D of 1.5 mA/μm, a G m of 0.77 mS/μm, a μe of 2100 cm2/V∙s, and a SS of 97 mV/dec. (20) The I D and G m of the In0.53Ga0.47As MOSFETs using in-situ MBE-GGO and -Y2O3 have set up records for enhancement-mode planar InGaAs MOSFETs (Fig. 1), as being benchmarked with the state-of-the-art enhanced mode (E-mode) devices. When the gate-stack engineering and gate length size scaling has continually reduced the on-state channel resistance, the contact resistance plays an important role of III-V MOSFETs. Our results in achieving low ohmic contacts, shown in Fig. 2 in the InGaAs MOSFETs, key for the high device performance, will also be discussed. Strong Fermi-level pinning (FLP) at metal/semiconductor (M-S) interface is found to be a major obstacle, resulting in the high Schottky barrier height (Φ bn,eff ) and contact resistance for electron transport. This serious FLP effect is attributed to the metal-induced gap states (MIGS) and bond polarization near the M-S interface. A solution for modulating the Φ bn,eff by Fermi-level (Ef ) depinning is to insert an ultra-thin dielectric between the metal and semiconductor as a metal-insulator-semiconductor (M-I-S) contact system. The ultra-low contact resistivity (ρc ) of 8 x 10-9 Ω.cm2 with the optimized insertion of a 0.6 nm ZnO dielectric between the contact metal (Al) and heavily Si-doped (1.5 x 1019 cm-3) InGaAs substrate is demonstrated in the Fig. 2(b) experimentally. (21,22) To whom the correspondence is addressed: mhong@phys.ntu.edu.tw (M. Hong), raynien@phys.nthu.edu.tw (J. Kwo), and pi@nsrrc.org.tw (T. W. Pi) Intl Technol. Roadmap for Semiconductors (ITRS) 2012. K. H. Shiu, et al, Appl. Phys. Lett. 92, 172904 (2008). M. Hong et al., J. Crystal Growth, 175-176, 422 (1997). M. Hong et al., Science, 283, 1897 (1999). F. Ren et al., Solid-State Electronics, 41, 1751 (1997). F. Ren et al., IEEE Electron Device Lett., 19, 309 (1998). Y. Xuan et al., IEEE IEDM, pp. 637-640 (2007). J. J. 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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.

The thermal stability in structural and electrical properties of HfO 2 , HfAlO x alloy, and Al 2 O 3 /HfO 2 stack thin films prepared by atomic layer deposition were comparatively investigated. Both HfAlO x and Al 2 O 3 /HfO 2 exhibit improved property against thermal degradation compared to the HfO 2 film. However, the incorporation of Al in alloy form provides characteristics superior to that in stack structure by retaining an amorphous structure up to 1000°C, which suppresses the leakage current and retards the growth of interfacial layer giving rise to lower increment of equivalent-oxide-thickness and interface trap density.

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