Che-Hao Chang

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...

Memory characteristics of au nanocrystals embedded in metal-oxide-semiconductor structure by using atomic-layer-deposited Al2O3 as control oxide

The nonvolatile memory characteristics of metal?oxide?semiconductor (MOS) structures containing Au nanocrystals in the Al2O3/SiO2 matrix were studied. In this work, we have demonstrated that the use of Al2O3 as control oxide prepared by atomic-layer-deposition enhances the erase speed of the MOS capacitors. A giant capacitance?voltage hysteresis loop and a very short erase time which is lower than 1?ms can be obtained. Compared with the conventional floating-gate electrically erasable programmable read-only memories, the erase speed was promoted drastically. In addition, very low leakage current and large turn-around voltage resulting from electrons or holes stored in the Au nanocrystals were found in the current?voltage relation of the MOS capacitors.

Charge storage characteristics of Au nanocrystals embedded in high-k gate dielectrics on Si

The charge storage characteristics of metal-oxide-semiconductor structures containing Au nanocrystals in atomic-layer-deposited high-k gate dielectrics were studied. Cross-sectional high-resolution transmission electron microscopy reveals that the Au nanocrystals are self-assembled in the high-k dielectric matrix after high temperature annealing in N2 ambient. The memory effect was observed from capacitance-voltage (C-V) relations and a satisfactory charge retention characteristic was obtained in the sample using Al2O3 as the gate dielectric than in the one using Hf2AlOx. Moreover, a saturation of electron storage in the metal-oxide-semiconductor capacitors was also observed.

Effect of Al Incorporation in the Thermal Stability of Atomic-Layer-Deposited HfO2 for Gate Dielectric Applications

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.

Ga2O3(Gd2O3) on Ge without interfacial layers: Energy-band parameters and metal oxide semiconductor devices

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.

Hydrous-Plasma Treatment of Pt Electrodes for Atomic Layer Deposition of Ultrathin High-k Oxide Films

Ultrathin Al 2 O 3 and HfO 2 uniform films of ∼7.3 nm thick were successfully grown by atomic layer deposition (ALD) on Pt electrodes in situ treated with hydrous plasma. X-ray photoelectron spectroscopy reveals that the Pt surface can be effectively modified to Pt(OH) 2 by the hydrous-plasma treatment. It improves the growth of the oxide films and reduces the leakage in the Al 2 O 3 and HfO 2 capacitors. The enhancement of hydrolysis reaction and chemisorption reactivity of the metal precursors on the hydroxylated surface of Pt is responsible for improvements in the growth and electrical properties of the ALD films.

Electron-wave quantum well energy band-pass filters

In this study, energy band-pass filters composed of superlattice resonance tunnelling structures are proposed. Based on the analogy between electron waves propagating in superlattice structures and electromagnetic waves travelling in transmission lines, the method developed for designing a coupled cavity filter in microwave engineering can be adopted to provide a first-cut design of energy band-pass filter to fulfil specific requirements. The governing equations are derived, and can be used to convert the parameters determined by the microwave technique to the physical dimensions of the quantum well structure. Then, adjustments are made such that the physical dimensions are integer multiples of the monolayer thickness, resulting in a change of the central energy of the pass-band. The potentials of the quantum well are fine tuned to compensate the shift of the centre energy. Designs of Butterworth single-cavity, Butterworth three-cavity and Chebyshev three-cavity energy band-pass filters are presented. The important feature of this energy band-pass filter is that the stop-band of this filter can be very wide so that spurious responses from out-of-band electrons can be reduced.

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.

High performance Ga 2 O 3 (Gd 2 O 3 )/Ge MOS devices without interfacial layers

Excellent electrical performances have been demonstrated for the MOSCAPs and MOSFETs using Ga<inf>2</inf>O<inf>3</inf>(Gd<inf>2</inf>O<inf>3</inf>) gate dielectrics deposited at room temperature on Ge(100) without employing any interfacial layers. In this work, we report a very low interfacial density of state (D<inf>it</inf>) of ∼2×10¹¹cm⁻²eV⁻¹, a low leakage current density (J<inf>g</inf>) of ∼10⁻⁹A/cm², well-behaved capacitance-voltage (C-V) characteristics including an excellent quasi-static C-V curve along with a high efficiency of 80% for the Fermi-level movement near the mid-gap. In addition, a high saturation drain current and a high transconductance of 496µA/µm and 178µS/µm, respectively, for the 1µm-gate-length device have been obtained as well.