High κ dielectric of HfAlO/HfO2 was an in-situ atomic-layer-deposited directly on molecular beam epitaxy grown In0.53Ga0.47As surface without using pre-treatments or interfacial passivation layers, where HfAlO (HfO2:Al2O3 ∼ 4:1) with high re-crystallization temperature was employed as the top oxide layer. The HfAlO (∼4.5 nm)/HfO2 (0.8 nm)/In0.53Ga0.47As metal oxide semiconductor capacitors have exhibited an oxide/In0.53Ga0.47As interface free of arsenic-related defective bonding, thermodynamic stability at 800 °C, and low leakage current densities of <10−7 A/cm2 at ±1 MV/cm. The interfacial trap density (Dit) spectra in absence of mid-gap peaks were obtained by temperature-dependent capacitance and conductance with Dit’s of 2–3 × 1012 eV−1 cm−2 below and 6–12 × 1011 eV−1 cm−2 above the mid-gap of In0.53Ga0.47As, respectively. An equivalent oxide thickness of less than 1 nm has been achieved by reducing the HfAlO thickness to ∼2.7 nm with the same initial HfO2 thickness of ∼0.8 nm.

InAs MOS devices passivated with molecular beam epitaxy (MBE)-grown Gd2O3 2–3 monolayers thick followed by an Al2O3 cap have demonstrated excellent electrical performances and interfacial properties. Band offset energies of in situ atomic-layer-deposited (ALD)-Al2O3/MBE-Gd2O3/InAs and ALD-Al2O3/InAs were determined by in situ x-ray photoelectron spectroscopy in conjunction with Fowler–Nordheim tunneling current analysis. A conduction-band offset energy (ΔEc) and a valence-band offset energy of 2.3 and 3.92 eV for ALD-Al2O3/InAs were determined, respectively. The insertion of a Gd2O3 layer increases the value of ΔEc by nearly 0.1 eV as compared to the case for Al2O3 directly deposited on InAs. The distribution of interfacial density of states (Dit) within the InAs bandgap, deduced by the conductance method at 77 K, gives a low Dit value of 1012 cm−2 eV−1 near the conduction-band edge. Moreover, with energy band engineering in the heterostructure, gate-first depletion channel InAs MOSFETs have produced drain current density of 46 μA/μm and transconductance of 17 μS/μm for 12-μm-gate-length devices at 300 K.

High κ gate dielectrics of HfO2 and Al2O3 were deposited on molecular beam epitaxy-grown In0.2Ga0.8As pristine surface using in-situ atomic-layer-deposition (ALD) without any surface treatment or passivation layer. The ALD-HfO2/p-In0.2Ga0.8As interface showed notable reduction in the interfacial density of states (Dit), deduced from quasi-static capacitance-voltage and conductance-voltage (G-V) at room temperature and 100 °C. More significantly, the midgap peak commonly observed in the Dit(E) of ALD-oxides/In0.2Ga0.8As is now greatly diminished. The midgap Dit value decreases from ≥15 × 1012 eV−1 cm−2 for ALD-Al2O3 to ∼2–4 × 1012 eV−1 cm−2 for ALD-HfO2. Further, thermal stability at 850 °C was achieved in the HfO2/In0.2Ga0.8As, whereas C-V characteristics of Al2O3/p-In0.2Ga0.8As degraded after the high temperature annealing. From in-situ x-ray photoelectron spectra, the AsOx, which is not the oxidized state from the native oxide, but is an induced state from adsorption of trimethylaluminum and H2O, was found at the ALD-Al2O3/In0.2Ga0.8As interface, while that was not detected at the ALD-HfO2/In0.2Ga0.8As interface.

Self-aligned inversion-channel In0.2Ga0.8As metal-oxide-semiconductor field-effect transistors (MOSFETs) with in situ molecular beam epitaxy grown Al2O3/Ga2O3(Gd2O3) (GGO) as a gate dielectric and a TiN metal gate have been fabricated on GaAs (100) substrates. A 4 μm gate-length MOSFET using a gate dielectric of Al2O3 (3 nm thick)/GGO (8 nm thick) demonstrates a maximum drain current of 9.5 μA/μm and an extrinsic transconductance of 3.9 μS/μm. The device performances are compared favorably with those of other inversion-channel GaAs MOSFETs on GaAs (100) and also of the device on GaAs (111)A substrates using atomic layer deposited Al2O3 as a gate dielectric.

Interfacial chemical analyses and electrical characterization of in situ atomic layer deposited (ALD) Al2O3 on freshly molecular beam epitaxy (MBE) grown n- and p- GaAs (001) with a (4×6) surface reconstruction are performed. The capacitance–voltage (C–V) characteristics of as-deposited and 550°CN2 annealed samples are correlated with their corresponding X-ray photoelectron spectroscopy (XPS) interfacial analyses. The chemical bonding for the as-deposited ALD-Al2O3/n- and p-GaAs interface is similar, consisting of Ga2O (Ga1+) and As-As bonding (As0) without any detectable arsenic oxides or Ga2O3; the interfacial chemical environments remained unchanged after 550°CN2 annealing for 1hr. Both as-deposited and annealed p-GaAs metal–oxide-semiconductor capacitors (MOSCAPs) exhibit C–V characteristics with small frequency dispersion (<5%). In comparison, n-GaAs MOSCAPs shows much pronounced frequency dispersion than their p-counterparts.

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.

Systematic temperature-dependent capacitance-voltage and conductance measurements were used to study the electrical characteristics of molecular beam epitaxy (MBE) and atomic layer deposition (ALD) oxides on In0.2Ga0.8As/GaAs. The distribution of interfacial density of states (Dit) within the band gap of In0.2Ga0.8As was deduced with the conductance method. The MBE-grown Ga2O3(Gd2O3)/In0.2Ga0.8As, with an excellent tailored interface, has given Dit values of ∼5×1011 eV−1 cm−2 above, ∼2×1012 eV−1 cm−2 below, and 1–7×1012 eV−1 cm−2 around the mid-gap region (0.5–0.7 eV above valence band maximum (EV)); the high Dit value near the mid-gap, extracted at 100 and 150 °C, may be related to the temperature effect, which tends to induce more trap excitations. In contrast, the ALD-Al2O3/In0.2Ga0.8As has yielded higher Dit values of>1013 eV−1 cm−2 around the mid-gap region.

In this work, without employing any IPL, excellent electrical performances for the Ge MOS devices, i.e. MOSCAPs and MOSFETs, have been demonstrated using ultra high vacuum (UHV) deposited Ga2O3(Gd2O3) [GGO] directly on Ge (100) with the incorporation of fluorine. The GGO/Ge interface is atomically abrupt with negligible Ge inter-diffusion and highly thermodynamically stable withstanding high temperature anneals as previously reported. We firstly fabricated the MOS devices with a thick GGO layer (~14nm) to carry out the charge pumping measurement for the extraction of convincing Dit's, along with the measurements on the MOSFET Furthermore, we examined the scalability of the GGO layer by reducing its thickness to ~3.5 nm with a thin Al2O3 cap for protection. Very good C-V characteristics and a GGO EOT of <; 1 nm have been achieved.

The metal-oxide-semiconductor (MOS) capacitors of Al2O3/Ga2O3(Gd2O3) on n- and p-type In0.2Ga0.8As with different metal gates exhibited excellent capacitance-voltage (C-V) characteristics and remarkable thermodynamic stability after rapid thermal annealing up to 850 degrees C. The flat-band voltage (V-fb), flat-band voltage shift (Delta V-fb), threshold voltage (V-th), and frequency dispersion of the MOS capacitors with different metal gates were extracted from the C-V curves. The V-th values of Al2O3/Ga2O3(Gd2O3)/p-In0.2Ga0.8As were calculated to be about 0.04 V (Al gate) and 1.15 V (Ni gate) and those of Al2O3/Ga2O3(Gd2O3)/n-In0.2Ga0.8As -1.94 V (Al gate) and -0.88 V (Ni gate). The correlation between flat-band voltage and different metal gates indicates unpinned Fermi levels at the metal/dielectric interfaces. (C) 2010 American Vacuum Society. [DOI: 10.1116/1.3271141]

High-κ dielectric Ga2O3(Gd2O3) (GGO) has been deposited on Ge (100) at room temperature using molecular beam epitaxy. In situ angular-resolved x-ray photoelectron spectroscopy on the GGO/Ge after gate dielectric deposition and 500°C postdeposition annealing has exhibited negligible Ge interdiffusion, thus revealing high thermal stability of the heterostructure. The CF4-plasma treatment on the passivated GGO/Ge has greatly improved the capacitance-voltage characteristics of the metal-oxide-semiconductor capacitors, besides the very low gate leakage current density of 3.2×10−9A∕cm2 at a flat-band voltage +1V. These excellent interfacial characteristics have been achieved without employing any intentional passivation layers.

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 3×1011cm−2eV−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 496μA/μm, 178μS/μm, and 389cm2/Vs in saturation drain current density, maximum transconductance, and effective hole mobility, respectively. The gate width and gate length of the MOSFET are 10μm and 1μm.

The metal-oxide-semiconductor (MOS) capacitors of Al2O3∕Ga2O3(Gd2O3) on n- and p-type In0.2Ga0.8As with different metal gates exhibited excellent capacitance-voltage (C-V) characteristics and remarkable thermodynamic stability after rapid thermal annealing up to 850°C. The flat-band voltage (Vfb), flat-band voltage shift (ΔVfb), threshold voltage (Vth), and frequency dispersion of the MOS capacitors with different metal gates were extracted from the C-V curves. The Vth values of Al2O3∕Ga2O3(Gd2O3)∕p-In0.2Ga0.8As were calculated to be about 0.04V (Al gate) and 1.15V (Ni gate) and those of Al2O3∕Ga2O3(Gd2O3)∕n-In0.2Ga0.8As −1.94V (Al gate) and −0.88V (Ni gate). The correlation between flat-band voltage and different metal gates indicates unpinned Fermi levels at the metal/dielectric interfaces.

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 Ga2O3(Gd2O3) and ALD-HfO2 on InGaAs have been achieved.

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 12μm gate-length depletion-mode n-channel InGaAs/GaAs MOSFET with a Ga2O3(Gd2O3) gate oxide 6nm thick shows an accumulated drain current density of 135mA/mm at Vg=2V. 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 175mA/mm at the same gate bias. In addition, there is a broader transfer characteristics and higher extrinsic peak transconductance of 48mS/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).