L. T. Tung

High-performance self-aligned inversion-channel In0.53Ga0.47As metal-oxide-semiconductor field-effect-transistor with Al2O3∕Ga2O3(Gd2O3) as gate dielectrics

Self-aligned inversion-channel In0.53Ga0.47As metal-oxide-semiconductor field-effect transistors (MOSFETs) using ultrahigh-vacuum deposited Al2O3∕Ga2O3(Gd2O3) (GGO) dual-layer dielectrics and a TiN metal gate were fabricated. For a In0.53Ga0.47As MOSFET using a gate dielectric of Al2O3(2nmthick)∕GGO(5nmthick), a maximum drain current of 1.05A∕mm, a transconductance of 714mS∕mm, and a peak mobility of 1300cm2∕Vs have been achieved, the highest ever reported for III-V inversion-channel devices of 1μm gate length.

Achieving a low interfacial density of states in atomic layer deposited Al2O3 on In0.53Ga0.47As

Atomic-layer-deposited Al2O3 on In0.53Ga0.47As with short air exposure between the oxide and semiconductor deposition has enabled the demonstration of nearly ideal frequency-dependent and quasistatic capacitance-voltage (C-V) characteristics. The excellent quasistatic C-V characteristics indicate a high efficiency of 63% for the Fermi-level movement near the midgap. A low mean interfacial density of states (D¯it)∼2.5×1011 cm−2 eV−1 was determined under 1 MHz using a charge pumping method, which was also employed to probe the depth profile of bulk traps (Nbt) and the energy dependence of Dit at 50 kHz: a low Nbt∼7×1018 cm−3 and a Dit of (2–4)×1011 cm−2 eV−1 in the lower half of the band gap and a higher Dit of ∼1012 cm−2 eV−1 in the upper half of the band gap. The employment of charge pumping method has given a more accurate determination of Dit, which is usually overestimated using other commonly methods such as the Terman, conductance, and high-low frequencies due to the influence of weak inversion at ro...

1nm equivalent oxide thickness in Ga2O3(Gd2O3)∕In0.2Ga0.8As metal-oxide-semiconductor capacitors

An equivalent oxide thickness about 1nm for Ga2O3(Gd2O3) (GGO) on In0.2Ga0.8As has been achieved by employing a thin in situ deposited 3nm thick Al2O3 protection layer. The dual gate oxide stacks of the Al2O3∕GGO (33, 20, 10, 8.5, and 4.5nm)/In0.2Ga0.8As∕GaAs metal-oxide-semiconductor (MOS) capacitors remain amorphous after rapid thermal annealing up to 800–850°C, accompanied with atomically sharp smooth oxide/semiconductor interfaces. Well behaved capacitance-voltage (C-V) curves of the MOS diodes have shown sharp transition from depletion to accumulation with small flatband voltage (1.1V for Au metal gate and 0.1V for Al), and weak frequency dispersion (1.5%–5.4%) between 10 and 500kHz at accumulation capacitance. Low leakage current densities [3.1×10−5 and 2.5×10−9A∕cm2 at V=Vfb+1V for Al2O3(3nm)∕GGO(4.5 and 8.5nm)], a high dielectric constant around 14–16 of GGO for all tested thicknesses, and a low interfacial density of states (Dit) in the low 1011cm−2eV−1 have also been accomplished.

Inversion-channel GaN metal-oxide-semiconductor field-effect transistor with atomic-layer-deposited Al2O3 as gate dielectric

Inversion n-channel GaN metal-oxide-semiconductor field-effect-transistors (MOSFETs) using atomic-layer-deposited Al2O3 as a gate dielectric have been fabricated, showing well-behaved drain I-V characteristics. The drain current was scaled with gate length (varying from 1to16μm), showing a maximum drain current of ∼10mA∕mm in a device of 1μm gate length, at a gate voltage of 8V and a drain voltage of 10V. At a drain voltage of 0.1V, a high Ion∕Ioff ratio of 2.5×105 was achieved with a very low off-state leakage of 4×10−13A∕μm. Both MOSFET and MOS capacitor showed very low leakage current densities of 10−8A∕cm2 at biasing fields of 4MV∕cm. The interfacial density of states was calculated to be (4–9)×1011cm−2eV−1 near the midgap.

Molecular beam epitaxy grown Ga2O3(Gd2O3) high κ dielectrics for germanium passivation-x-ray photoelectron spectroscopy and electrical characteristics

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.

Al2O3/Ga2O3(Gd2O3) passivation on In0.20Ga0.80As/GaAs-structural intactness with high-temperature annealing

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.

Oxide scalability in Al2O3∕Ga2O3(Gd2O3)∕In0.20Ga0.80As∕GaAs heterostructures

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.

Growth and structural characteristics of GaN∕AlN/nanothick γ-Al2O3∕Si (111)

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.

Inversion-channel GaN MOSFET using atomic-layer-deposited Al 2 O 3 as gate dielectric

For the first time, inversion-channel GaN MOSFETs using atomic-layer-deposited (ALD) Al<inf>2</inf>O<inf>3</inf> as a gate dielectric have been successfully fabricated, showing well-behaved drain I–V and transfer characteristics. The drain current was scaled with gate length, showing a maximum drain current of 10 mA/mm in a device of 1 µm gate length, at a gate voltage (V<inf>gs</inf>) of 8 V and a drain voltage (V<inf>ds</inf>) of 10V. High I<inf>on</inf>/I<inf>off</inf> ratio of 2.5×10⁵ was achieved with a very low off-state leakage of 4×10⁻¹³A/µm. In addition, depletion-mode (D-mode) GaN MOSFETs have also been demonstrated, showing a very low on-resistance of 2.5 mΩ⋅cm², a high mobility of 350 cm²/Vs, and a high maximum drain current of 300 mA/mm in a device of 4 µm gate length.

Metal-oxide-semiconductor devices with UHV-Ga 2 O 3 (Gd 2 O 3 ) on Ge(100)

Ultra-high vacuum (UHV)-deposited high Ga<inf>2</inf>O<inf>3</inf>(Gd<inf>2</inf>O<inf>3</inf>) was proved to passivate Ge effectively, as evidenced by comprehensive investigations including structural, chemical, and electrical analyses. The Ga<inf>2</inf>O<inf>3</inf>(Gd<inf>2</inf>O<inf>3</inf>)/Ge interface is revealed to be abrupt even being subjected to a 500°C anneal, a high κ value of 14.5, a low leakage current density of ∼10<inf>−9</inf>A/cm² with a Fowler-Nordheim tunneling behavior, and well-behaved C-V characteristics are achieved. Furthermore, Ge self-aligned pMOSFETs with Al<inf>2</inf>O<inf>3</inf>/ Ga<inf>2</inf>O<inf>3</inf>(Gd<inf>2</inf>O<inf>3</inf>) as the gate dielectrics have demonstrated a high drain current and a peak transconductance up to 252mA/mm and 143mS/mm, respectively, of 1µm-gate length.