Shin-Yuan Wang

DOPING EFFECT ON NORMAL INCIDENT INGAAS/GAAS LONG-WAVELENGTH QUANTUM WELL INFRARED PHOTODETECTORS

8–12 μm InGaAs/GaAs quantum well infrared photodetectors with two different well doping concentrations have been studied. The devices with and without surface gratings are compared for normal incident operation. It is found that the TE to TM absorption ratio depends on the doping density in the quantum wells. A higher doping density increases TE absorption. A detectivity about 1×1010 cm Hz1/2/W and a peak responsivity of 0.23 A/W at 9 μm have been obtained for the grating-free devices.8–12 μm InGaAs/GaAs quantum well infrared photodetectors with two different well doping concentrations have been studied. The devices with and without surface gratings are compared for normal incident operation. It is found that the TE to TM absorption ratio depends on the doping density in the quantum wells. A higher doping density increases TE absorption. A detectivity about 1×1010 cm Hz1/2/W and a peak responsivity of 0.23 A/W at 9 μm have been obtained for the grating-free devices.

Self-assembled In0.22Ga0.78As quantum dots grown on metamorphic GaAs/Ge/SixGe1-x/Si substrate

Self-assembled In0.22Ga0.78As quantum dots (QDs) grown on Si substrate with Ge∕SiGe as buffer layer grown by metal organic vapor phase epitaxy were investigated. Transmission electron microscopy and atomic force microscopy images were used to observe the size and space distribution of the In0.22Ga0.78As QDs grown on the GaAs∕Ge∕GeSi∕Si layer structure. The influence of the growth temperature on the QDs size and density distribution was investigated. For QDs grown at 450°C, the density of the In0.22Ga0.78As dots was estimated to be 1×1011cm−2 and the In0.22Ga0.78As QDs thickness was 5 ML (monolayer) thick.

Nonuniform quantum well infrared photodetectors

A nonuniform quantum well infrared photodetector (QWIP) structure is proposed. By changing the doping concentration and barrier width of each quantum well, the electric field distribution can be tailored. The nonuniform QWIPs show excellent performance compared with conventional uniform structures. The dark current is about an order of magnitude lower and the background limited temperature increases to 77 K. A detectivity of 2.0×1010 cm Hz1/2/W and a responsivity of 0.25 A/W at 8.2 μm have been obtained for these devices. A simple picture of electric field distribution within the structure is described to explain the results.

OPTICAL AND STRUCTURAL PROPERTIES OF EPITAXIALLY LIFTED-OFF GAAS FILMS

The influence of the layer thickness on the optical and structural properties of the epitaxially lifted-off (ELO) thin films has been studied. The ELO films bonded to Si, InP, and GaAs substrates have also been compared. The structure was characterized by high-resolution double-crystal x-ray diffraction and the optical properties were measured by the temperature-dependent photoluminescence spectroscopy. A biaxial compressive strain was observed for the samples bonded to Si with a buffer layer thinner than 1000 nm. Due to different thermal expansion coefficient between the grafted thin film and the host substrate, the emission spectra of the quantum wells of the lifted-off thin films are redshifted compared to the as-grown sample. The amount of the redshift is larger for thinner films.

Interface Characterization of HfO 2 /GaSb MOS Capacitors With Ultrathin Equivalent Oxide Thickness by Using Hydrogen Plasma Treatment

We investigate p-type GaSb MOS capacitors with various HfO2 thicknesses grown using an atomic layer deposition. GaSb surfaces treated with ex-situ chemical solution and in situ remote hydrogen plasma are inspected. After a series of etching steps, the GaSb surfaces exhibit smooth topography, indicating that this combination of treatments is capable of realizing ultrathin dielectric deposition. After etching processes, the ultrathin (approximately 3 nm) HfO2 layer deposited successfully on GaSb exhibit high-permittivity (approximately 21) properties as well as equivalent oxide thickness (EOT) of 0.75 nm, which can be attributed to the flat surface. To the best of our knowledge, the EOT of GaSb capacitor prepared using the exploited approach is record low. Furthermore, we find that the interlayer present after hydrogen plasma treatment and forming gas annealing could efficiently passivate interface state density and achieve high C-V modulation. Compared with the benchmark of gate leakage current versus EOT, the electrical performance with low gate leakage current of the GaSb MOS capacitors demonstrates the high feasibility of the proposed treatments.

Electrical Characteristics of MOSCAPs and the Effect of Postdeposition Annealing Temperatures

The characteristics of Al2O3/InSb MOSCAPs processed with different postdeposition annealing (PDA) temperatures are investigated. X-ray photoelectron spectroscopy analysis shows a significant reduction of InSb-oxides after HCl plus trimethyl aluminum treatment and oxide deposition. Multifrequency capacitance-voltage (C-V) characteristics exhibit low-frequency and asymmetrical C-V behaviors, in which capacitance in the InSb conduction band side is lower than in the valence band side. The electrical properties of the MOSCAPs are sensitive to PDA temperature and degraded significantly at PDA temperature >300 °C. This degradation is closely related to the diffusion of In, Sb into Al2O3 as indicated by transmission electron microscopy analyses.

Demonstrating 1 nm-oxide-equivalent-thickness HfO2/InSb structure with unpinning Fermi level and low gate leakage current density

In this work, the band alignment, interface, and electrical characteristics of HfO2/InSb metal-oxide-semiconductor structure have been investigated. By using x-ray photoelectron spectroscopy analysis, the conduction band offset of 1.78 ± 0.1 eV and valence band offset of 3.35 ± 0.1 eV have been extracted. The transmission electron microscopy analysis has shown that HfO2 layer would be a good diffusion barrier for InSb. As a result, 1 nm equivalent-oxide-thickness in the 4 nm HfO2/InSb structure has been demonstrated with unpinning Fermi level and low leakage current of 10−4 A/cm−2. The Dit value of smaller than 1012 eV−1cm−2 has been obtained using conduction method.

Hot-electron relaxation via optical phonon emissions in GaAs/AlxGa1-xAs quantum well structures: dependence upon the alloy composition and barrier width

We present a systematic investigation of the dependence of the hot-electron-optical-phonon interactions on Al composition and barrier width in GaAs/AlxGa1-xAs MQW structures. Raman scattering measurements at 15 K are presented for samples with different barrier widths and Al composition. The optical phonon energies emitted by the photoexcited electrons in quantum wells were also determined by using hot-electron-neutral acceptor luminescence techniques. It is shown that the relaxation of hot electrons in the quantum wells is dominated by the GaAs LO phonon emission for small x, but by AlAs-like LO phonons for larger Al composition. For samples with larger barriers, the electrons in the GaAs layer relax mostly through the AlAs-like optical phonon emission. However, in samples with smaller barriers, the relaxation of hot electrons is dominated by the GaAs optical phonon emission.

Integration of microwave-annealed oxidation on germanium metal-oxide-semiconductor devices

In this paper, a method that entails using microwave thermal oxidation to form a high-quality gate dielectric on Ge through surface passivation at considerably low temperatures (<400 °C) is presented. Formation of the GeOx layer was confirmed by x-ray photoelectron spectroscopy. To reduce the bulk trap density and interface trap density (Dit), microwave thermal oxidation was employed for postdeposition microwave thermal oxidation after the deposition of Al2O3 through atomic layer deposition. Tiny frequency dispersion in capacitance measurement and a low Dit value of 5.9 × 1011 cm−2 eV−1 near the midgap confirmed a desirable passivation effect, which was favorable in mitigating the formation of dangling bonds on the Ge surface. A small hysteresis in capacitance was also observed, suggesting that the bulk dielectric was of high quality. On the basis of these characteristics, microwave-activated GeOx is a promising passivation layer material for aggressively scaled Ge-related metal oxide semiconductor devices.In this paper, a method that entails using microwave thermal oxidation to form a high-quality gate dielectric on Ge through surface passivation at considerably low temperatures (<400 °C) is presented. Formation of the GeOx layer was confirmed by x-ray photoelectron spectroscopy. To reduce the bulk trap density and interface trap density (Dit), microwave thermal oxidation was employed for postdeposition microwave thermal oxidation after the deposition of Al2O3 through atomic layer deposition. Tiny frequency dispersion in capacitance measurement and a low Dit value of 5.9 × 1011 cm−2 eV−1 near the midgap confirmed a desirable passivation effect, which was favorable in mitigating the formation of dangling bonds on the Ge surface. A small hysteresis in capacitance was also observed, suggesting that the bulk dielectric was of high quality. On the basis of these characteristics, microwave-activated GeOx is a promising passivation layer material for aggressively scaled Ge-related metal oxide semiconductor devices.

Integration of hetero-structure body-tied Ge FinFET using retrograde-well implantation

In this work, we investigated the influence of retrograde-well implantation on hetero-structure body-tied germanium (Ge) FinFET [1]. Using structural engineering, the retrograde well was fabricated prior to Ge epitaxy, which could avoid the activated temperature of dopant in Si substrate. With optimizing the implant condition, the p-Ge/n-Si hetero-structure junction exhibited high I_ON/I_OFF ratio and lower junction leakage (4 × 10^-3 μA/cm²). Furthermore, we also make a comparison of planar and mesa junction structures, mesa junction exhibited lower junction leakage (6× 10^-6 μA/cm²) as compared with the planar one mentioned before, which could be attributed to improvement in peripheral leakage due to dislocation within Ge and Si. Comparing the difference between retrograde-well and implant-free Ge FinFETs, the drain induced barrier lowering (DIBL) was considerably improved by 50 %. Our retrograde-well Ge FinFET exhibited a high I_ON/I_OFF ratio ~ 8×10³ (I_S) than the conventional Ge FinFET (I_ON/I_OFF ~2×10³).