Y.H. Chang

III–V Metal–Oxide–Semiconductor Field-Effect Transistors with High κ Dielectrics

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 Dits 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 (MOSFETs). The oxide remains amorphous and the interface remains intact with atomic smoothness and sharpness. Device performances of inversion-channel and depletion-mode III–V MOSFETs are reviewed, again with emphasis on the devices using Ga2O3(Gd2O3) as the gate dielectric.

Attainment of low interfacial trap density absent of a large midgap peak in In0.2Ga0.8As by Ga2O3(Gd2O3) passivation

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.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.

Observation of room temperature ferromagnetic behavior in cluster-free, Co doped HfO2 films

Extensive structural and magnetic analyses of Hf1−xCoxO2 thin films grown by molecular beam epitaxy are reported. Nearly cobalt cluster-free film with x=0.04–0.1 was obtained via 100°C growth, and Co ions are inferred to be located at interstitial site. Ferromagnetic behavior was observed up to 300K in both magnetization curves and temperature dependence of the moment. Via post-oxygen-annealing studies, a qualitative correlation between saturation magnetization and oxygen vacancy concentration is established, consistent with the impurity-band exchange model, and that the occurrence of ferromagnetic insulator behavior in the Co doped HfO2 is more probable than Co doped ZnO, TiO2, and SnO2 systems for doping concentrations under cation percolation threshold.

The effect of temperature on the epitaxial quality of bilayers of iridium silicide and SiGe deposited on Si(100) in ultrahigh vacuum

Ir-silicide/SiGe layers were co-deposited on a p-Si(100) substrate at high temperatures. Reflection high energy electron diffraction, transmission electron microscope, and grazing angle incidence X-ray diffraction have been used in characterizing the co-deposited layers. Heteroepitaxial Ir-silicide/SiGe layers on top of p-Si(100) have been achieved at a substrate temperature of 450°C. The Ir-silicide layer was determined to be Ir3Si4 with four types of epitaxial modes. The three principal axes (a = 18.551 A, b = 3.840 A, and c = 5.713 A) were found to be strained, slightly different from those in the bulk Ir3Si4 (a = 18.870 A, b = 3.679 A, and c = 5.774 A). The Ir-silicide/SiGe layers co-deposited at 550 and 525°C showed dual phases and polycrystalline structures. corresponding to three-dimensional island growth.

Achieving a Low Interfacial Density of States with a Flat Distribution in High-κ Ga2O3(Gd2O3) Directly Deposited on Ge

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.

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.

Nano-electronics of high κ dielectrics on InGaAs for key technologies beyond Si CMOS

The surface Fermi level unpinning in InGaAs has been realized with high κ dielectric growth using molecular beam eitaxy (MBE) and atomic layer deposition (ALD). Furthermore, world-record device performances in self-aligned inversion-channel InGaAs MOSFET and a capacitance equivalent thickness (CET) of ≤ 1 nm in Ga<inf>2</inf>O<inf>3</inf>(Gd<inf>2</inf>O<inf>3</inf>) and ALD-HfO<inf>2</inf> on InGaAs have been achieved.

Heteroepitaxy of PtSi/SiGe on Si(100) by dual electron gun co-deposition at high temperatures

Abstract Co-deposition of both PtSi and SiGe layers on a p-Si(100) substrate has been performed at high temperatures in a dual electron gun deposition chamber at a base pressure of 10-10 Torr. Reflection high energy electron diffraction, transmission electron microscope, and X-ray diffraction have been used in characterizing the epitaxial film. The PtSi/SiGe film co-deposited at a substrate temperature of 450°C had four types of epitaxial modes. Two of them were the same as the epitaxial modes for the PtSi film formed by depositing Pt on Si with sequential annealing. The other two epitaxial modes were observed in the PtSi/SiGe/p- Si(100) for the first time. The PtSi film co-deposited at 550°C showed polycrystalline structures, corresponding to three-dimensional island growth.

Nano-electronics of high k dielectrics on exotic semiconductors for science and technology beyond Si CMOS

We have achieved high device performance in self-aligned inversion-channel InGaAs MOSFETs, as well as a CET of < 1 nm, a D<inf>it</inf> ≤ 10¹¹ eV⁻¹cm⁻², and high-temperature thermal stability withstanding >850°C RTA in GGO and a CET of < 1 nm in ALD-HfO<inf>2</inf> on InGaAs. Remarkable device performances in self-aligned, inversion-channel Ge MOSFET using GGO without any interfacial passivation layers (IPLs), and inversion-channel and accumulation type GaN MOSFETs with high ks as gate dielectrics have also been attained. Interfacial characteristics including energy band parameters were studied using x-ray photoelectron spectroscopy (XPS).

Self-aligned inversion-channel In 0.75 Ga 0.25 As MOSFETs using MBE-Al 2 O 3 /Ga 2 O 3 (Gd 2 O 3 ) and ALD-Al 2 O 3 as gate dielectrics

High-performance self-aligned inversion-channel In<inf>0.75</inf>Ga<inf>0.25</inf>As n-MOSFETs using in-situ ultra-high-vacuum (UHV) deposited Al<inf>2</inf>O<inf>3</inf>/Ga<inf>2</inf>O<inf>3</inf>(Gd<inf>2</inf>O<inf>3</inf>) and ex-situ atomic-layer-deposited (ALD) Al<inf>2</inf>O<inf>3</inf> as gate dielectrics have been fabricated. Both devices exhibit excellent DC characteristics, including high drain currents and transconductances. A 1.2µm-gate-length In<inf>0.75</inf>Ga<inf>0.25</inf>As MOSFET using Al<inf>2</inf>O<inf>3</inf>(2nm-thick)/GGO(13nm-thick) dual-layer gate dielectric demonstrated a maximum drain current of 970 µA/µm, a peak transconductance of 410 µS/µm, and a peak mobility of 1560 cm²/V·s. A maximum drain current of 194 µA/µm and a peak transconductance of 126 µS/µm were exhibited by a 2µm-gate-length In<inf>0.75</inf>Ga<inf>0.25</inf>As MOSFET using ALD-Al<inf>2</inf>O<inf>3</inf>(6nm-thick).