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ABSTRACT: The interfacial electronic structure of Ga2O3(Gd2O3) (GGO) on n-Ge(001) is determined using high-resolution synchrotron radiation photoemission. The excitation photon energy was specifically chosen to observe the interaction at the GGO/Ge interface (hv = 463 eV) as well as the possible diffusion of Ge up to the GGO surface (hν = 120 eV). The Ge 3d core-level spectra were fit to extract the contributing components. Photoemission measurements were done for four samples, as deposited, N2 annealed, CF4 plasma treated, and the combined CF4 plasma treated and N2 annealed. No surface passivation was employed prior to the dielectric deposition. SRPES data clearly showed that the elemental Ge in the as-deposited sample was effectively kept in the wafer. Prevention of Ge diffusion was attributed to formation of a thin germanatelike oxide layer. Other than contributions from bulk Ge, an analytical fit to the Ge 3d cores gives two components that are associated with bonding to Gd2O3 (GdGe*) and to Ga2O3 (GaGe*), which had chemical shifts of 3.46 and 1.80 eV, respectively. We hereby label them as MGe*, where M stands for either Gd2O3 or Ga2O3. Area occupations of the GdGe* and GaGe* oxides are ∼87% and ∼10%, respectively. A CF4 plasma treatment disturbs the film itself as well as the interfacial oxide so that the GGO surface begins to show both elemental Ge and Ga. Nevertheless, the follow-up N2 annealing produces the GdGe*+GaGe* layer with characteristics similar to those at the GGO/Ge interface. Both GdGe* and GaGe* states in the CN-treated sample show simultaneously a smaller chemical shift by 0.31 ± 0.02 eV than those in the as-deposited sample. The treatments also induce upward band bending on both the high κ and the Ge sides, which causes the valence band offset at the GGO/Ge interface to be 2.95 eV.
Journal of Applied Physics 03/2011; 109(6):063725-063725-6. · 2.17 Impact Factor
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C. A. Lin,
H. C. Chiu,
T. H. Chiang, T. D. Lin,
Y. H. Chang,
W. H. Chang,
Y. C. Chang,
W.-E. Wang,
J. Dekoster,
T. Y. Hoffmann,
M. Hong,
J. Kwo
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ABSTRACT: The pronounced high interfacial densities of states (Dit) commonly observed around the midgap energy of dielectric/GaAs interfaces are generally considered the culprit responsible for the poor electrical performance of the corresponding inversion-channel metal-oxide-semiconductor field-effect-transistors. In this work, comprehensive Dit spectra as the function of energy [Dit(E)] inside the In0.2Ga0.8As band gap were constructed by using the quasistatic capacitance-voltage and the temperature-dependent conductance method on n- and p-type ultrahigh vacuum (UHV)-Ga2O3(Gd2O3)/In0.2Ga0.8As and atomic-layer-deposited (ALD)-Al2O3/In0.2Ga0.8As metal-oxide-semiconductor capacitors. Unlike the ALD-Al2O3/In0.2Ga0.8As interface giving a Dit spectrum with a high midgap Dit peak, the UHV-Ga2O3(Gd2O3)/In0.2Ga0.8As interface shows a Dit spectrum that monotonically decreases from the valence band to the conduction band with no discernible midgap peak.
Applied Physics Letters 02/2011; 98(6):062108-062108-3. · 3.84 Impact Factor
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ABSTRACT: Ga2O3(Gd2O3) (GGO) directly deposited on Ge substrate in ultrahigh vacuum, without a passivation layer such as GeOxNy or Si, has demonstrated excellent electrical performances and thermodynamic stability. Energy-band parameters of GGO/Ge have been determined by in situ x-ray photoelectron spectroscopy in conjunction with reflection electron energy loss spectroscopy and current transport of Fowler–Nordheim tunneling. A conduction-band offset and a valence-band offset of ∼ 2.3 and ∼ 2.42 eV, respectively, have been obtained. Moreover, self-aligned Ge pMOSFETs of 1-μm-gate length using Al2O3/GGO as the gate dielectrics have shown a high drain current and a peak transconductance of 252 mA/mm, and 143 mS/mm, respectively.
Applied Physics Letters 05/2009; 94(20):202108-202108-3. · 3.84 Impact Factor
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ABSTRACT: X-ray photoelectron spectroscopy (XPS) combined with reflection electron energy loss spectroscopy (REELS) were used to determine the energy-band parameters, valence-band offsets ΔE<sub>V</sub> , conduction-band offsets ΔE<sub>C</sub> , and energy-band gaps E<sub>g</sub> , of the atomic layer deposited (ALD) Al <sub>2</sub> O <sub>3</sub> and HfO <sub>2</sub> on In <sub>x</sub> Ga <sub>1-x</sub> As ( x=0 , 0.15, 0.25, and 0.53). Using REELS, E<sub>g</sub> values of the ALD-Al <sub>2</sub> O <sub>3</sub> and – HfO <sub>2</sub> were estimated to be 6.77 and 5.56±0.05 eV , respectively. The ΔE<sub>V</sub> ’s were determined by measuring the core level to valence band maximum binding energy difference from the XPS spectra. The ΔE<sub>C</sub> ’s were then extracted from ΔE<sub>V</sub> ’s and the energy-band gaps of the oxides and In <sub>x</sub> Ga <sub>1-x</sub> As , and are in good agreement with those estimated from the Fowler–Nordheim tunneling. The ΔE<sub>C</sub> ’s and ΔE<sub>V</sub> ’s are larger than 1.5 and 2.5 eV, respectively, for all the ALD-oxide/ In <sub>x</sub> Ga <sub>1-x</sub> As samples.
Applied Physics Letters 03/2009; · 3.84 Impact Factor
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ABSTRACT: Electrical characteristics of oxide-In<sub>0.2</sub>Ga<sub>0.8</sub>As interface in ultra-high vacuum (UHV)-deposited Al<sub>2</sub>O<sub>3</sub>(3 nm)/Ga<sub>2</sub>O<sub>3</sub> (Gd<sub>2</sub>O<sub>3</sub>) (8.5 nm) on n- and p-In<sub>0.2</sub>Ga<sub>0.8</sub>As/GaAs are studied. Capacitance-voltage ( C-V ) measurements under light illumination and under wide range of temperatures as well as corresponding conductance-voltage ( G-V ) measurements were carried out. Extremely high-quality interfaces with free-moving Fermi-level near the conductance and valence band-edges (regions close to E<sub>c</sub> and E<sub>v</sub>) are revealed for the Ga<sub>2</sub>O<sub>3</sub>(Gd<sub>2</sub>O<sub>3</sub>)/In<sub>0.2</sub>Ga<sub>0.8</sub>As system.
Electron Devices Meeting, 2008. IEDM 2008. IEEE International; 01/2009
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ABSTRACT: Self-aligned inversion-channel In <sub>0.53</sub> Ga <sub>0.47</sub> As metal-oxide-semiconductor field-effect transistors (MOSFETs) using ultrahigh-vacuum deposited Al <sub>2</sub> O <sub>3</sub>/ Ga <sub>2</sub> O <sub>3</sub>( Gd <sub>2</sub> O <sub>3</sub>) (GGO) dual-layer dielectrics and a TiN metal gate were fabricated. For a In <sub>0.53</sub> Ga <sub>0.47</sub> As MOSFET using a gate dielectric of Al <sub>2</sub> O <sub>3</sub>(2 nm thick )/ GGO (5 nm thick ) , a maximum drain current of 1.05 A / mm , a transconductance of 714 mS / mm , and a peak mobility of 1300 cm <sup>2</sup>/ V s have been achieved, the highest ever reported for III-V inversion-channel devices of 1 μ m gate length.
Applied Physics Letters 08/2008; · 3.84 Impact Factor
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ABSTRACT: Atomic-layer-deposited high κ dielectric Hf O <sub>2</sub> films on air-exposed In <sub>0.53</sub> Ga <sub>0.47</sub> As / In P (100), using Hf ( N C H <sub>3</sub> C <sub>2</sub> H <sub>5</sub>)<sub>4</sub> and H <sub>2</sub> O as the precursors, were found to have an atomically sharp interface free of arsenic oxides, an important aspect for Fermi level unpinning. A careful and thorough probing, using high-resolution angular-resolved x-ray photoelectron spectroscopy (XPS) with synchrotron radiation, however, observed the existence of Ga <sub>2</sub> O <sub>3</sub> , In <sub>2</sub> O <sub>3</sub> , and In ( O H )<sub>3</sub> at the interface. The current transport of the metal-oxide-semiconductor capacitor for an oxide 7.8 nm thick follows the Fowler–Nordheim tunneling mechanism and shows a low leakage current density of ∼10<sup>-8</sup> A / cm <sup>2</sup> at V<sub> FB </sub>+1 V . Well behaved frequency-varying capacitance-voltage curves were measured and an interfacial density of states of 2×10<sup>12</sup> cm <sup>-2</sup> eV <sup>-1</sup> was derived. A conduction-band offset of 1.8±0.1 eV and a valence-band offset of 2.9±0.1 eV have been determined using the current transport data and X-
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PS, respectively.
Applied Physics Letters 03/2008; · 3.84 Impact Factor
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ABSTRACT: The aggressive scaling of Si CMOS device has called for high κ dielectrics and metal gates. However, the phonon issue related to the high κ gate dielectrics has lead to degraded channel mobility. Extensive research activities are now being taken on channel materials, such as InGaAs, with mobility higher than that of Si. In 0.53 Ga 0.47 As, lattice matched to InP, and In 0.15 Ga 0.85 As, strained growth on GaAs, have been used as a backbone for almost all the high-speed electronic devices in high electron mobility transistor (HEMT) with very high cutoff frequency. Oxide gates may improve device performance, e.g. in reducing gate leakage and increasing I on /I off ratio. Atomic layer deposited (ALD) high κ dielectric HfO 2 films on air-exposed In 0.53 Ga 0.47 As/InP and In 0.15 Ga 0.85 As /GaAs were found to have an atomically sharp interface, free of arsenic oxides, which is believed to attribute to the Fermi level un-pinning. The energy band parameters were measured for HfO 2 /In 0.53 Ga 0.47 As and HfO 2 /In 0.15 Ga 0.85 As, respectively. Figure 1 (a)-(b) show the HR-TEM for air-exposed In 0.53 Ga 0.47 As and ALD-HfO 2 / In 0.53 Ga 0.47 As, respectively. The detailed chemical state and distribution, including arsenic or arsenic oxides are studied using XPS, as shown in Fig. 2 (a)-(c). After the ALD-HfO 2 growth, As 2 O 3 was removed from the oxide/InGaAs interface. No arsenic oxides (As 2 O 3 or As 2 O 5) were found to be on top of the as-grown ALD-HfO 2 . The detection of Ga 2 O 3 , In 2 O 3 , and In(OH) 3 at the HfO 2 -InGaAs interface was made possible with HR-XPS using synchrotron radiation or with AR (angle-resolved)-XPS. An abrupt transition from InGaAs to ALD-HfO 2 with a thin interfacial layer was observed using HR-TEM. The similar results were observed for air-exposed In 0.15 Ga 0.85 As and ALD-HfO 2 / In 0.15 Ga 0.85 As, respectively. The removal of the arsenic oxides from HfO 2 /InGaAs heterostructures during ALD process ensures the Fermi level unpinning, which was observed in the C-V measurements. As illustrated in Fig. 3, C-V curves for In 0.53 Ga 0.47 As show accumulation and inversion. The C-V at 1 kHz shows a similar behavior as the C-V of Si MOS diodes at 1 or 10Hz, namely the occurrence of inversion. In contrast, C-V curves show much larger frequency dispersion for In 0.15 Ga 0.85 As sample (Fig. 4). Low leakage current densities of ~10 -7 to 10 -9 A/cm 2 at electrical fields less than 4 MV/cm (Fig.5) were measured for the 7.8 nm HfO 2 on In 0.53 Ga 0.47 As/InP, annealed at 375°C for 60 min in forming gas. The current transport of the MOS device can be explained by the Fowler-Nordheim tunneling mechanism. Similar transport properties were measured on In 0.15 Ga 0.85 As /GaAs. The conduction-band offset of ~ 1.8 and 1.48eV were determined for HfO 2 /In 0.53 Ga 0.47 As and HfO 2 / In 0.15 Ga 0.85 As, respectively. The valence band offset at the HfO 2 /In 0.53 Ga 0.47 As and HfO 2 / In 0.15 Ga 0.85 As interface was determined using XPS to be ~2.9 eV and ~2.65 eV, respectively, as shown in Fig. 6. The energy band parameters determined from XPS and the transport measurement are listed in Fig. 7. There is no surface cleaning and interfacial passivation layer prior to the ALD-HfO 2 . However, the oxide/InGaAs interface is atomically sharp without the existence of arsenic oxides, strongly indicating self-cleaning of the ALD process. Excellent well-behaved J-E G and C-V characteristics of ALD-HfO 2 / In 0.53 Ga 0.47 As/InP have been demonstrated in this work.
01/2008;
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ABSTRACT: In this paper, there is no surface cleaning and interfacial passivation layer prior to the ALD-HfO<sub>2</sub>. However, the oxide/InGaAs interface is atomically sharp without the existence of arsenic oxides, strongly indicating self-cleaning of the ALD process. Excellent well-behaved J-E<sub>G</sub> and C-V characteristics of ALD-HfO<sub>2</sub>/In<sub>0.53</sub>Ga<sub>0.47</sub>As/InP have been demonstrated in this work.
Semiconductor Device Research Symposium, 2007 International; 01/2008
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ABSTRACT: A dual-layer gate dielectric approach for application in III-V metal-oxide-semiconductor field-effect transistor (MOSFET) was studied by using ultrahigh vacuum deposited 7–8 nm thick Ga <sub>2</sub> O <sub>3</sub>( Gd <sub>2</sub> O <sub>3</sub>) as the initial dielectric to unpin the surface Fermi level of In <sub>0.18</sub> Ga <sub>0.82</sub> As and then molecular-atomic deposition of ∼2–3 nm thick Si <sub>3</sub> N <sub>4</sub> as a second dielectric protecting Ga <sub>2</sub> O <sub>3</sub>( Gd <sub>2</sub> O <sub>3</sub>) . The total equivalent oxide thickness achieved in this study is 5 nm . We have demonstrated an enhancement mode In <sub>0.18</sub> Ga <sub>0.82</sub> As / Ga As MOSFET with surface inverted n channel with drain current (I<sub>d</sub>) of 0.1 mA for a gate length of 10 μ m and a gate width of 880 μ m at V<sub> ds </sub>=1 V and V<sub>g</sub>=4.5 V .
Applied Physics Letters 12/2007; · 3.84 Impact Factor
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ABSTRACT: Ga 2 O 3 (Gd 2 O 3), a high κ gate dielectric, ultrahigh vacuum (UHV)-deposited on GaAs and InGaAs has unpinned the Fermi level in the high-electron-mobility III–V compound semiconductors for the first time. Systematic heat treatments under various gases and temperatures were studied to achieve low leakage currents of 10 − 8 –10 − 9 A/cm 2 and low interfacial density of states (D it' s) in the range of b 10 11 cm − 2 eV − 1 . By removing moisture from the oxide, thermodynamic stability of the Ga 2 O 3 (Gd 2 O 3)/GaAs heterostructures and the interfaces were achieved with high temperature annealing, the oxide remains amorphous and the interface remains intact with atomic smoothness and sharpness. The Fermi-level unpinning in atomic layer deposition (ALD) Al 2 O 3 ex-situ deposited on InGaAs was achieved. Recent work of extremely high-quality nano-thick single crystal oxides of gamma-Al 2 O 3 and bixbyite cubic Sc 2 O 3 epitaxially grown on Si (111) is discussed. Interfacial manipulation is essential in giving excellent results presented in the paper. X-ray diffraction, reflectivity, and X-ray photoelectron spectroscopy using synchrotron radiation are critical in probing the interfacial properties.
03/2007;
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ABSTRACT: An interfacial self-cleaning phenomenon was found in the atomic layer deposition of Hf O <sub>2</sub> on In <sub>0.15</sub> Ga <sub>0.85</sub> As / Ga As substrate using Hf ( N C H <sub>3</sub> C <sub>2</sub> H <sub>5</sub>)<sub>4</sub> , i.e., TEMAH, and H <sub>2</sub> O as the precursors. The native oxides of InGaAs were all satisfactorily removed from the interface through ligand exchange (substitution) reactions with the TEMAH precursor. It relieves the Fermi-level pinning in the Hf O <sub>2</sub>/ In Ga As heterostructure, as verified by the clear transition from accumulation to depletion in high-frequency capacitance-voltage relations and inversion in quasistatic measurement. A very low leakage current was also found from the metal-oxide-semiconductor capacitors of Au / Ti / Hf O <sub>2</sub>/ In Ga As .
Applied Physics Letters 01/2007; · 3.84 Impact Factor
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ABSTRACT: The valence-band offset has been determined to be 3.83±0.05 eV at the atomic-layer-deposition Al <sub>2</sub> O <sub>3</sub>/ In Ga As interface by x-ray photoelectron spectroscopy. The Au – Al <sub>2</sub> O <sub>3</sub>/ In Ga As metal-oxide-semiconductor diode exhibits current-voltage characteristics dominated by Fowler-Nordheim tunneling. From the current-voltage data at forward and reverse biases, a conduction-band offset of 1.6±0.1 eV at the Al <sub>2</sub> O <sub>3</sub>– In Ga As interface and an electron effective mass ∼0.28±0.04m<sub>0</sub> of the Al <sub>2</sub> O <sub>3</sub> layer have been extracted. Consequently, combining the valence-band offset, the conduction-band offset, and the energy-band gap of the InGaAs, the energy-band gap of the atomic-layer-deposited Al <sub>2</sub> O <sub>3</sub> is 6.65±0.11 eV .
Applied Physics Letters 08/2006; · 3.84 Impact Factor
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ABSTRACT: High κ Ga2O3(Gd2O3) dielectric was deposited on n-type GaN (0 0 0 1) using molecular beam epitaxy (MBE). TiN/Ga2O3(Gd2O3)/GaN metal–oxide–semiconductor (MOS) diodes have exhibited a negligible frequency dispersion, low leakage currents (∼10−8 A/cm2), and a low interfacial density of states (Dit) of 1011 cm−2 eV−1 at the midgap. Well-behaved capacitance–voltage (CV) curves with accumulation and depletion behaviors were shown, with a dielectric constant of 14.7. Forming gas annealing at 600 °C has reduced the frequency dispersion in the CV curves. A sharp oxide/semiconductor interface was shown by high-resolution transmission electron microscopy (HR-TEM).
Journal of Crystal Growth · 1.73 Impact Factor
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ABSTRACT: A self-aligned process for fabricating inversion n-channel metal–oxide–semiconductor field-effect-transistors (MOSFET’s) of strained In0.2Ga0.8As on GaAs using TiN as gate metal and Ga2O3(Gd2O3) as high κ gate dielectric has been developed. A MOSFET with a 4 μm gate length and a 100 μm gate width exhibits a drain current of 1.5 mA/mm at Vg = 4 V and Vd = 2 V, a low gate leakage of <10−7 A/cm2 at 1 MV/cm, an extrinsic transconductance of 1.7 mS/mm at Vg = 3 V, Vd = 2 V, and an on/off ratio of ∼105 in drain current. For comparison, a TiN/Ga2O3(Gd2O3)/In0.2Ga0.8As MOS diode after rapid thermal annealing (RTA) to high temperatures of 750 °C exhibits excellent electrical and structural performances: a low leakage current density of 10−8–10−9 A/cm2, well-behaved capacitance–voltage (C–V) characteristics giving a high dielectric constant of ∼16 and a low interfacial density of state of ∼(2∼6) × 1011 cm−2 eV−1, and an atomically sharp smooth Ga2O3(Gd2O3)/In0.2Ga0.8As interface.
Solid-State Electronics. 52(10):1615-1618.
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ABSTRACT: Without using any interfacial passivation layers, high-κ dielectric Y2O3, HfO2, and Ga2O3(Gd2O3) [GGO], by electron beam evaporation in ultra-high-vacuum (UHV), have been directly deposited on Ge substrate. Comprehensive investigations have been carried out to study the oxide/Ge interfaces chemically, structurally, and electronically: hetero-structures of all the studied oxides on Ge are highly thermally stable with annealing to 500 °C, and their interfaces remain atomically sharp. The electrical analyses have been conducted on metal–oxide–semiconductor (MOS) devices, i.e. MOS capacitors (MOSCAPs) and MOS field-effect-transistors (MOSFETs). Dielectrics constants of the Y2O3, HfO2, and GGO have been extracted to be ∼17, 20, and 13–15, respectively, indicating no interfacial layer formation with 500 °C annealing. A low interfacial density of states (Dits), as low as 3 × 1011 cm−2 eV−1, has been achieved for GGO/Ge near mid-gap along with a high Fermi-level movement efficiency as high as 80%. The GGO/Ge pMOSFETs with TiN as the metal gate have yielded very high-performances, in terms of 496 μA/μm, 178 μS/μm, and 389 cm2/V s in saturation drain current density, maximum transconductance, and effective hole mobility, respectively. The gate width and gate length of the MOSFET are 10 μm and 1 μm.
Solid-State Electronics. 54(9):965-971.
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ABSTRACT: Self-aligned inversion-channel In0.75Ga0.25As metal-oxide-semiconductor field-effect transistors (MOSFETs) using molecular beam epitaxy (MBE) deposited Al2O3/Ga2O3(Gd2O3) [GGO] as gate dielectrics and TiN as metal gates were fabricated. The 1-μm-gate-length In0.75Ga0.25As MOSFETs have achieved a maximum drain current of 1.23 mA/μm, a peak transconductance of 464 μS/μm, and a peak field-effect electron mobility of 1600 cm2/V s. A new record of maximum drain current has been set, not only for III–V MOSFETs but also for all enhancement mode MOSFETs with similar device dimensions, regardless of channel materials and device configurations.
Journal of Crystal Growth 323(1):518-521. · 1.73 Impact Factor
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ABSTRACT: 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-Ga2O3(Gd2O3) as the gate dielectric are compared favorably with those using the gate dielectrics made from other thin film techniques.
Journal of Crystal Growth 323(1):511-517. · 1.73 Impact Factor
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ABSTRACT: A nearly lattice-matched Gd2O3/Si(1 1 1) hetero-epitaxy was demonstrated using molecular beam epitaxy (MBE). Detailed structural studies find that the nano thick Gd2O3 films have a cubic phase with a very uniform thickness, an excellent crystallinity and atomically sharp interfaces. These features are characterized by the bright, streaky reconstructed reflection high-energy electron diffraction (RHEED) patterns at the initial oxide growth, the pronounced interference fringes in the X-ray reflectivity curve as well as in the crystal truncation rod around the substrate diffraction peaks using the high-resolution X-ray diffraction. The (1 1 1) axis of the thin oxide is oriented parallel to the substrate (1 1 1) normal with a 60° in-plane symmetry rotation.
Journal of Crystal Growth · 1.73 Impact Factor
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ABSTRACT: Depletion-mode In0.2Ga0.8As/GaAs metal-oxide-semiconductor field-effect transistors (MOSFETs) were fabricated with molecular beam epitaxy (MBE) grown Al2O3/Ga2O3(Gd2O3) as the gate dielectric in two comparable processes. In the “metal-gate-last” process, a 12 μm gate-length depletion-mode n-channel InGaAs/GaAs MOSFET with a Ga2O3(Gd2O3) gate oxide 6 nm thick shows an accumulated drain current density of 135 mA/mm at Vg=2 V. In the other process of “metal-gate-first” process, the device with same gate dielectric, channel, and gate length exhibits a larger drain current density of 175 mA/mm at the same gate bias. In addition, there is a broader transfer characteristics and higher extrinsic peak transconductance of 48 mS/mm in the metal-gate-first process. MOS capacitors from both processes have exhibited excellent capacitance–voltage (C–V) characteristics with minor dispersion, negligible hysteresis, and κ values of 13.7–13.9 in Ga2O3(Gd2O3).
Journal of Crystal Growth 311(7):1954-1957. · 1.73 Impact Factor
