Zhaoqi Sun

Modulating the Interface Quality and Electrical Properties of HfTiO/InGaAs Gate Stack by Atomic-Layer-Deposition-Derived Al2O3 Passivation Layer

In current work, the effect of the growth cycles of atomic-layer-deposition (ALD) derived ultrathin Al2O3 interfacial passivation layer on the interface chemistry and electrical properties of MOS capacitors based on sputtering-derived HfTiO as gate dielectric on InGaAs substrate. Significant suppression of formation of Ga-O and As-O bond from InGaAs surface after deposition of ALD Al2O3 with growth cycles of 20 has been achieved. X-ray photoelectron spectroscopy (XPS) measurements have confirmed that suppressing the formation of interfacial layer at HfTiO/InGaAs interface can be achieved by introducing the Al2O3 interface passivation layer. Meanwhile, increased conduction band offset and reduced valence band offset have been observed for HfTiO/Al2O3/InGaAs gate stack. Electrical measurements of MOS capacitor with HfTiO/Al2O3/InGaAs gate stacks with dielectric thickness of ∼4 nm indicate improved electrical performance. A low interface-state density of (∼1.9) × 10(12) eV(-1) cm(-2) with low frequency dispersion ( ∼ 3.52%), small border trap density of 2.6 × 10(12) cm(-2), and low leakage current of 1.17 × 10(-5) A/cm(2) at applied gate voltage of 1 V have been obtained. The involved leakage current conduction mechanisms for metal-oxide-semiconductor (MOS) capacitor devices with and without Al2O3 interface control layer also have been discussed in detail.

Facile synthesis of iron oxides/reduced graphene oxide composites: application for electromagnetic wave absorption at high temperature

Iron oxides/reduced graphene oxide composites were synthesized by facile thermochemical reactions of graphite oxide and FeSO4·7H2O. By adjusting reaction temperature, α-Fe2O3/reduced graphene oxide and Fe3O4/reduced graphene oxide composites can be obtained conveniently. Graphene oxide and reduced graphene oxide sheets were demonstrated to regulate the phase transition from α-Fe2O3 to Fe3O4 via γ-Fe2O3, which was reported for the first time. The hydroxyl groups attached on the graphene oxide sheets and H2 gas generated during the annealing of graphene oxide are believed to play an important role during these phase transformations. These samples showed good electromagnetic wave absorption performance due to their electromagnetic complementary effect. These samples possess much better electromagnetic wave absorption properties than the mixture of separately prepared Fe3O4 with rGO, suggesting the crucial role of synthetic method in determining the product properties. Also, these samples perform much better than commercial absorbers. Most importantly, the great stability of these composites is highly advantageous for applications as electromagnetic wave absorption materials at high temperatures.

Interface control and modification of band alignment and electrical properties of HfTiO/GaAs gate stacks by nitrogen incorporation

Effects of nitrogen incorporation on the interface chemical bonding states, optical dielectric function, band alignment, and electrical properties of sputtering-derived HfTiO high-k gate dielectrics on GaAs substrates have been studied by angle resolved X-ray photoemission spectroscopy (ARXPS), spectroscopy ellipsometry (SE), and electrical measurements. XPS analysis has confirmed that the interfacial layer of a HfTiO/GaAs gate stack is suppressed effectively after nitrogen incorporation. Analysis by SE has confirmed that reduction in band gap and increase in refractive index are observed with the incorporation of nitrogen. Reduction in valence band offset and increase in conduction band offset have been observed for a HfTiON/GaAs gate stack. Electrical measurements based on metal-oxide-semiconductor (MOS) capacitors have shown that the MOS capacitor with a HfTiON/GaAs stacked gate dielectric annealed at 600 °C exhibits low interface-state density (2.8 × 1012 cm−2 eV−1), small gate leakage current (2.67 × 10−5 A cm−2 at Vg = Vfb + V), and large dielectric constant (25.8). The involved mechanisms may originate from the decrease in the interface state density and the increase in the conduction band offset. The appropriate band offset relative to GaAs and excellent interface properties render HfTiON/GaAs as promising gate stacks in future III–V-based devices.

Effect of dimethylaluminumhydride-derived aluminum oxynitride passivation layer on the interface chemistry and band alignment of HfTiO-InGaAs gate stacks

In this letter, the reduction and removal of surface native oxide from as-received InGaAs surface by using dimethylaluminumhydride-derived aluminum oxynitride (AlON) passivation layer prior to HfTiO deposition is proposed to solve Fermi level pinning issue. It has been revealed that complete consumption of native oxides of AsOx and GaOx at the InGaAs surface, but no effect to InOx, has been realized after metalorganic chemical vapor deposition AlON at 300 °C. X-ray photoelectron spectroscopy observations of HfTiO/InGaAs gate stacks demonstrate that introducing AlON layer can suppress the regrowth of native oxide at the interface. In addition, the dependence of the valence band spectra of HfTiO/InGaAs gate stacks on AlON passivation layer has been discussed in detail.

Review and Perspective of Hf-based High-k Gate Dielectrics on Silicon

HfO2 has been recently highlighted as the most promising high-k dielectrics for the next-generation CMOS device applications due to its relatively high dielectric constant and superior thermodynamic stability from calculated Gibbs free reaction with Si. However, the high permeability to oxygen, the low crystallization temperature and the formation of the low-k interfacial layer during high temperature processing causes equivalent oxide thickness scaling and reliability concerns. Therefore, novel Hf-based high-k gate dielectrics should be studied to meet the requirements of the future advanced CMOS devices. This article provides a comprehensive view of the state-of-the-art research activities in advanced Hf-based high-k gate dielectrics, including their preparation, characterization, and potential applications in CMOS device. We begin with a survey of the requirements of high-k oxides, and then various methods developed for generating Hf-based high-k gate dielectrics. After that, more attention has been paid to the detailed discussion of on the latest development of novel Hf-based high-k gate dielectrics which have the potential for integration into a full CMOS process. Finally, we conclude this review with the perspectives and outlook on the future developments in this area. This review explores the possible influences of research breakthroughs of Hf-based gate dielectrics on the current and future applications for nano-MOSFET devices.

Nitrogen dependence of band alignment and electrical properties of HfTiON gate dielectrics metal-oxide-semiconductor capacitor

The effect of nitrogen incorporation on the band alignment and electrical properties of HfTiO gate dielectric complementary metal-oxide-semiconductor (MOS) capacitors has been investigated by spectroscopy ellipsometry, x-ray photoelectron spectroscopy, and electrical measurements. Reduction in optical band gap and band offsets has been detected. However, improved electrical properties have been achieved from HfTiON gate dielectric MOS capacitors attributed to the nitrogen-induced reduction in oxygen-related traps and the improved interface quality. Although there is a nitrogen-induced reduction in band gap and band offset, the sufficient barrier heights still makes HfTiON a promising high-k gate dielectric candidate for proposed near-future complementary metal-oxide-semiconductor applications.

Rational Design of α-Fe2O3/Reduced Graphene Oxide Composites: Rapid Detection and Effective Removal of Organic Pollutants

α-Fe2O3/reduced graphene oxide (α-Fe2O3/rGO) composites are rationally designed and prepared to integrate organic pollutants detection and their photocatalytic degradation. Specifically, the composites are used as the substrate for surface-enhanced Raman scattering (SERS) to detect rhodamine 6G (R6G). Repeatable strong SERS signals could be obtained with R6G concentration as low as 10(-5) M. In addition, the substrate exhibits self-cleaning properties under solar irradiation. Compared with pure α-Fe2O3 and α-Fe2O3/rGO mechanical mixtures, the α-Fe2O3/rGO composites show much higher photocatalytic activity and much greater Raman enhancement factor. After 10 cycling measurements, the photodegradation rate of R6G could be maintained at 90.5%, indicating high stability of the photocatalyst. This study suggests that the α-Fe2O3/rGO composites would serve both as recyclable SERS substrate and as excellent visible light photocatalyst.

HfO2–GaAs metal-oxide-semiconductor capacitor using dimethylaluminumhydride-derived aluminum oxynitride interfacial passivation layer

In this letter, treatment of GaAs surface by using dimethylaluminumhydride-derived AlON passivation layer prior to HfO2 deposition is proposed to solve the issue of Fermi level pinning. It has been found that AlON passivation layer effectively suppresses the oxides formation and leads to the Fermi level unpinning at the interface between GaAs and HfO2. Based on analysis from metal-oxide-semiconductor capacitors of Au/HfO2/AlON/GaAs stack, excellent capacitance-voltage characteristics with saturated accumulation capacitance and reduced leakage current have been achieved, which may originate from the decrease in the interface state density and the increase in the conduction band offset.

CVD-derived Hf-based High-k Gate Dielectrics

Hf-based high-k gate dielectric has been recently highlighted as the most promising high-k dielectrics for the next-generation CMOS devices with high performance due to its excellent thermal stability and relatively high dielectric constant. This article provides a comprehensive view of the state-of-the-art research activities in advanced Hf-based high-k gate dielectrics grown by chemical-vapor-deposition-based method, including metal-organic-chemical-vapor-deposition (MOCVD), atomic-layer-chemical-vapor-deposition (ALCVD), and plasma-enhanced- chemical-vapor-deposition (PECVD), in CMOS device. We begin with a survey of methods developed for generating Hf-based high-k gate dielectrics. After that, most attention has been paid to the detailed discussion of the latest development of novel Hf-based high-k gate dielectrics grown by CVD. Finally, we conclude this review with the perspectives and outlook on the future developments in this area. This article explores the possible influences of research breakthroughs of Hf-based gate dielectrics on the current and future applications for nano-MOSFET devices.

WO3 and Ag nanoparticle co-sensitized TiO2 nanowires: preparation and the enhancement of photocatalytic activity

In this paper, TiO2 nanowires decorated with WO3 nanoparticles (WO3-TWS) on Ti foils were prepared using simple hydrothermal treatment, wet impregnation and subsequent annealing treatment, sequentially. Ag nanoparticles were successfully deposited on the obtained WO3-TWS by a successive ionic layer adsorption reaction technique. Ultraviolet-visible absorption spectra showed that the introduction of Ag and WO3 particles on TiO2 nanowire surfaces extends the absorption edge to the visible light regime. More importantly, the increase of Ag content greatly enhances the absorption intensity in the visible light regime. The photocatalytic experiment results revealed that TiO2 nanowires decorated with Ag and WO3 nanoparticles possess higher photocatalytic activities toward methyl orange than pure TiO2 nanowires. The degradation percentage of 95.6% after 10 cycles indicated that the as-prepared photocatalyst composites exhibited excellent long-time recyclability for the degradation of contaminants.