T. H. Chiang

Effective passivation of In0.2Ga0.8As by HfO2 surpassing Al2O3 via in-situ atomic layer deposition

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 fo...

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.

Surface Passivation of GaSb(100) Using Molecular Beam Epitaxy of Y2O3 and Atomic Layer Deposition of Al2O3: A Comparative Study

Y2O3 and Al2O3 were deposited onto GaSb(100) surfaces by molecular beam epitaxy and atomic layer deposition, respectively. Angle-resolved X-ray photoelectron spectroscopy and electrical measurements were used to probe the two oxide/semiconductor interfaces, which yielded very different behaviors. Highly surface-sensitive scans showed traces of SbOx and AsOx at the Y2O3 surface, which were removed during subsquent ALD Al2O3. The deposition of Y2O3 led to true inversion as indicated in capacitance–voltage (C–V) characteristics, small hysteresis and frequency dispersion, and low gate leakage. In contrast, for Al2O3/GaSb, the GaSb remained virtually intact, with Al2O3 bonding to the residual As, leading to poor C–V characteristics.

Approaching fermi level unpinning in Oxide-In0.2Ga0.8As

Electrical characteristics of oxide-In_0.2Ga_0.8As interface in ultra-high vacuum (UHV)-deposited Al₂O₃(3 nm)/Ga₂O₃ (Gd₂O₃) (8.5 nm) on n- and p-In_0.2Ga_0.8As/GaAs are studied. Capacitance-voltage (<i>C-V</i>) measurements under light illumination and under wide range of temperatures as well as corresponding conductance-voltage (<i>G-V</i>) measurements were carried out. Extremely high-quality interfaces with free-moving Fermi-level near the conductance and valence band-edges (regions close to E_c and E_v) are revealed for the Ga₂O₃(Gd₂O₃)/In_0.2Ga_0.8As system.

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.

High-resolution core-level photoemission study of CF4-treated Gd2O3(Ga2O3) gate dielectric on Ge probed by synchrotron radiation

High-resolution core-level photoemission analysis using synchrotron radiation was used to investigate the superior electrical performance of aGa 2 O 3 ( Gd 2 O 3 ) gate dielectric on Ge(001) after CF 4 treatment. Prior to the treatment, a thin germanate-like oxide layer that formed at the interface prevented Ge from diffusing to the surface. The Gesurface retained a small amount of buckled dimers from the as-grown sample. The buckled dimers were quickly removed by CF 4 plasma treatment followed by an annealing process, resulting in a more uniform interface than that of the as-grown sample. The detailed interfacial electronic structure for the untreated and treated samples are presented.

Engineering of threshold voltages in molecular beam epitaxy-grown Al2O3∕Ga2O3(Gd2O3)∕In0.2Ga0.8As

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.

Single crystal Gd2O3 epitaxially on GaAs(111)A

Gd2O3 films 2 and 6 nm thick, electron-beam evaporated from a compact powder target, were deposited on freshly molecular beam epitaxy (MBE) grown epi-GaAs(111)A in a multi-chamber MBE system. The oxide films are epitaxial with the underlying GaAs, as studied by in situ reflective high energy electron diffraction and high-resolution X-ray diffraction using synchrotron radiation. The films undergo a structure phase transformation from hexagonal to monoclinic when the film thickness increases from 2 to 6 nm; the 2 nm oxide has H-Gd2O3(0001)[100]‖GaAs(111)[4] orientation relationship and the 6 nm film follows M-Gd2O3(01)[102]‖GaAs(111) with 3 rotational variants anchored by the 3-fold symmetric substrate. Here, H and M denote the hexagonal and monoclinic phases, respectively.

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.

Optimization of Ohmic metal contacts for advanced GaAs-based CMOS device

Ohmic contact resistivity of a nongold Pd/Ge/Ti/Pt on highly doped molecular beam epitaxy grown n-GaAs and In0.2Ga0.8As/GaAs (∼2 × 1018 cm−3) has been investigated by varying Pd/Ge thicknesses and rapid thermal annealing (RTA) temperature/duration. An optimized Ohmic contact was obtained in the samples with Pd/Ge of 30 nm/30 nm, using RTA at 300 °C for 10 s. Low Ohmic contact resistivity of 5.4 × 10−7 Ω cm2 on n-In0.2Ga0.8As has been achieved. The mechanism of the contact resistivity reduction has been studied using the energy-dispersive x-ray spectroscopy depth profile.