Mao-Lin Huang

Surface passivation of III-V compound semiconductors using atomic-layer-deposition-grown Al2O3

Al2O3 was deposited on In0.15Ga0.85As∕GaAs using atomic-layer deposition (ALD). Without any surface preparation or postthermal treatment, excellent electrical properties of Al2O3∕InGaAs∕GaAs heterostructures were obtained, in terms of low electrical leakage current density (10−8 to 10−9A∕cm2) and low interfacial density of states (Dit) in the range of 1012cm−2eV−1. The interfacial reaction and structural properties studied by high-resolution x-ray photoelectron spectroscopy (HRXPS) and high-resolution transmission electron microscopy (HRTEM). The depth profile of HRXPS, using synchrotron radiation beam and low-energy Ar+ sputtering, exhibited no residual arsenic oxides at interface. The removal of the arsenic oxides from Al2O3∕InGaAs heterostructures during the ALD process ensures the Fermi-level unpinning, which was observed in the capacitance-voltage measurements. The HRTEM shows sharp transition from amorphous oxide to single crystalline semiconductor.

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.

Nanometer-Thick Single-Crystal Hexagonal Gd2 O3 on GaN for Advanced Complementary Metal-Oxide-Semiconductor Technology.

Hexagonal-phase single-crystal Gd2 O3 is deposited on GaN in a molecular beam epitaxy system. The dielectric constant is about twice that of its cubic counterpart when deposited on InGaAs or Si. The capacitive effective thickness of 0.5 nm in hexagonal Gd2 O3 is perhaps the lowest on GaN-metal-oxide-semiconductor devices. The heterostructure is thermo dynamically stable at high temperatures and exhibits low interfacial densities of states after high-temperature annealing.

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.

Self-Aligned Inversion-Channel In0. 53Ga0. 47As Metal--Oxide--Semiconductor Field-Effect Transistors with In-situ Deposited Al2O3/Y2O3 as Gate Dielectrics

In-situ ultrahigh-vacuum-deposited Y2O3 2–3-monolayer-thick on freshly grown In0.53Ga0.47As with an Al2O3 cap were employed as a gate dielectric. A low interfacial density of states of (8–9)×1011 eV-1 cm-2 near the midgap has been measured using the conductance method. The strong Y2O3/InGaAs interfacial bonding, revealed using X-ray photoelectron spectroscopy, enables attainment of an atomically smooth interface with 750 °C annealing. Low subthreshold swing of 97 mV/decade, high drain current of 1.5 mA/µm, high transconductance of 0.77 mS/µm, and field-effect mobility of 2,100 cm2 V-1 s-1 were achieved in a self-aligned inversion-channel InGaAs metal–oxide–semiconductor field-effect-transistor of 1 µm gate length.

Structural and compositional investigation of yttrium-doped HfO2 films epitaxially grown on Si (111)

Cubic phase yttrium-doped HfO2 (YDH) ultrathin films were grown on Si (111) substrates by molecular beam epitaxy. Thorough structural and morphological investigations by x-ray scattering and transmission electron microscopy reveal that the YDH thin films are epitaxially grown on the Si substrates with (111)YDH‖(111)Si and [101¯]YDH‖[11¯0]Si. The interface between YDH and Si is atomistic sharp and free of interfacial layer. We have also determined the yttrium content of YDH films to be 19% by using anomalous x-ray diffraction (AXD) across Y k edge and angle resolved x-ray photoelectron spectroscopy (AR-XPS). The agreement between the AXD and AR-XPS results manifests that the incorporated Y atoms homogeneously substitute Hf atoms in the crystalline lattice and form a substitutional solid solution.

Molecular beam epitaxy grown template for subsequent atomic layer deposition of high κ dielectrics

Molecular beam epitaxy (MBE) grown high κ dielectrics of Al2O3 and HfO2 are employed as templates to suppress effectively the oxide/Si interfacial layer formation during the subsequent atomic layer deposition (ALD) growth. The absence of the interfacial layer was confirmed using x-ray photoelectron spectroscopy and high resolution transmission electron microscopy. Two composite films consisting of ALDAl2O3(1.9nm)∕MBEAl2O3(1.4nm) and ALDAl2O3(3.0nm)∕MBEHfO2(2.0nm) showed overall κ values of 9.1 and 11.5, equivalent oxide thicknesses of 1.41 and 1.7nm, Dit of 2.2×1011 and 2×1011cm−2eV−1, and leakage current densities of 2.4×10−2A∕cm2 at Vfb−1V and 1.1×10−4A∕cm2 at Vfb+1V, respectively. The attainment of high dielectric constant suggests that there is no low κ capacitor in series near the oxide/Si interface.

Si metal-oxide-semiconductor devices with high κ HfO2 fabricated using a novel MBE template approach followed by atomic layer deposition

Molecular beam epitaxy (MBE) was employed to grow nanothick high κ HfO2 films on Si (100) as templates to suppress the formation of the oxide/Si interfacial layer during the subsequent atomic layer deposited (ALD) HfO2 growth. A metal-oxide-semiconductor (MOS) diode with the ALD/MBE bilayer stack of an equivalent oxide thickness (EOT) of ∼1.1nm has demonstrated markedly low electrical leakage of 8.3×10−3A∕cm2 at Vfb−1V, a reduction by five order of magnitudes, comparing with those using SiO2 of the same EOT. The attainment of high dielectric constant and very small frequency dispersion in capacitance-voltage (C-V) curves suggests the absence of low κ capacitors in series near the oxide/Si interface. Furthermore, MOS field-effect transistors (MOSFETs) based on the ALD/MBE-HfO2 composites have been fabricated having excellent device performance, with a drain current (ID) of 240mA∕mm and transconductance (Gm) of 120mS∕mm. These are superior to those of the MOSFETs using either ALD (55mA∕mm, 60mS∕mm) or MBE (...