Hudong Chang

Compounds and phase relations in the SrO-Fe2O3-CuO, SrO-Fe2O3-Gd2O3 and Gd2O3-Fe2O3-CuO ternary systems

The subsolidus phase relations in the SrO-Fe2O3-CuO, SrO-Fe2O3-Gd2O3 and Gd2O3-Fe2O3-CuO systems have been investigated by the means of X-ray powder diffraction (XRD). All samples were synthesized in the air at 960 degreesC. There are nine binary compounds in the system SrO-Fe2O3-CuO. This system can be divided into twelve three-phase regions. A new ternary compound Sr7Fe17CuO34 is identified. There are eight binary compounds and no ternary compound in the SrO-Fe2O3-Gd2O3 system. Nine three-phase regions lie in this system. In the Gd2O3-Fe(2)9O(3)-CuO system, there are four binary compounds and no ternary compound. This system can be divided into five three-phase regions. The crystal structure of the binary compound SrGd2O4 was determined by powder XRD, this compound belongs to an orthorhombic structure with space group Pnma. The lattice parameters are a = 10.1226(1) Angstrom, b = 3.4720(0) c = 12.0482(2) Angstrom

High performance GaN-based LEDs on patterned sapphire substrate with patterned composite SiO 2 /Al 2 O 3 passivation layers and TiO 2 /Al 2 O 3 DBR backside reflector

GaN-based light-emitting diodes (LEDs) on patterned sapphire substrate (PSS) with patterned composite SiO(2)/Al(2)O(3) passivation layers and TiO(2)/Al(2)O(3) distributed Bragg reflector (DBR) backside reflector have been proposed and fabricated. Highly passivated Al(2)O(3) layer deposited on indium tin oxide (ITO) layer with excellent uniformity and quality has been achieved with atomic layer deposition (ALD) technology. With a 60 mA current injection, an enhancement of 21.6%, 59.7%, and 63.4% in the light output power (LOP) at 460 nm wavelength was realized for the LED with the patterned composite SiO(2)/Al(2)O(3) passivation layers, the LED with the patterned composite SiO(2)/Al(2)O(3) passivation layers and Ag mirror + 3-pair TiO(2)/SiO(2) DBR backside reflector, and the LED with the patterned composite SiO(2)/Al(2)O(3) passivation layer and Ag mirror + 3-pair ALD-grown TiO(2)/Al(2)O(3) DBR backside reflector as compared with the conventional LED only with a single SiO(2) passivation layer, respectively.

Al2O3/GeOx gate stack on germanium substrate fabricated by in situ cycling ozone oxidation method

Al2O3/GeOx/Ge gate stack fabricated by an in situ cycling ozone oxidation (COO) method in the atomic layer deposition (ALD) system at low temperature is systematically investigated. Excellent electrical characteristics such as minimum interface trap density as low as 1.9 × 1011 cm−2 eV−1 have been obtained by COO treatment. The impact of COO treatment against the band alignment of Al2O3 with respect to Ge is studied by x-ray photoelectron spectroscopy (XPS) and spectroscopic ellipsometry (SE). Based on both XPS and SE studies, the origin of gate leakage in the ALD-Al2O3 is attributed to the sub-gap states, which may be correlated to the OH-related groups in Al2O3 network. It is demonstrated that the COO method is effective in repairing the OH-related defects in high-k dielectrics as well as forming superior high-k/Ge interface for high performance Ge MOS devices.

A High Performance In0.7Ga0.3As MOSFET with an InP Barrier Layer for Radio-Frequency Application

We demonstrate a high performance implant-free n-type In0.7Ga0.3As channel MOSFET with a 4-nm InP barrier layer fabricated on a semi-insulating substrate employing a 10-nm Al2O3 as gate dielectric. The maximum effective channel mobility is 1862 cm(2)/V.s extracted by the split C V method. Devices with 0.8 mu m gate length exhibit a peak extrinsic transconductance of 85mS/mm and a drive current of more than 200mA/mm. A short-circuit current gain cutoff frequency f(T) of 24.5 GHz and a maximum oscillation frequency f(max) of 54 GHz are achieved for the 0.8 mu m gate-length device. The research is helpful to obtain higher performance In0.7Ga0.3As MOSFETs for radio-frequency applications.

High-Performance GaN-Based Light-Emitting Diodes on Patterned Sapphire Substrate with a Novel Patterned SiO2/Al2O3 Passivation Layer

GaN-based light-emitting diodes (LEDs) on patterned sapphire substrate (PSS) with a novel patterned SiO2/Al2O3 passivation layer have been proposed and fabricated. Due to the excellent uniformity and compactness of atomic layer deposition (ALD) for the first Al2O3 layer, a high passivation effect has been achieved. The second SiO2 layer with patterned hemisphere arrays decreases the total internal reflection (TIR) and, hence, increases the light output power (LOP). With a 60 mA injection current, an enhancement of 21.6% in LOP was realized for the LED with an appropriately patterned SiO2/Al2O3 passivation layer as compared with the conventional LED with a SiO2 passivation layer.

Extrinsic Base Surface Passivation in Terahertz GaAsSb/InP DHBTs Using InGaAsP Ledge Structures

Type-II GaAsSb/InP double heterojunction bipolar transistors (DHBTs) with a novel InGaAsP ledge structure were studied utilizing a 2-D hydrodynamic physical device model for the first time. The proposed ultrathin InGaAsP ledge design provides a simple and effective approach to suppress the emitter size effect and enables nanoscale GaAsSb/InP DHBTs to further increase the operating frequencies and integration levels for submillimeter-wave applications.

Crystal structure and physical properties of FeSr2GdCu2O7+δ

A new Fe–Sr–Gd–oxide–cuprate compound FeSr2GdCu2O7+δ (Fe1212) was successfully synthesized by solid-state reaction. X-Ray diffraction data indicate that the sample is single phase. A Rietveld refinement of the structure was carried out. This compound has a 1212-type structure of a tetragonal symmetry. The lattice parameters are a=3.8457(1) A, c=11.3875(2) A and the space group is P4/mmm. Magnetization measurements show that this compound exhibits paramagnetic behavior above 5 K. Resistance measurements show that the sample has a semiconductor-like behavior.

A comparative study of Ge MOSFET using Al 2 O 3 /GeO x /Ge stacks-forming high quality GeO x interface layer to boost device performance

Ge is a promising candidate to replace Si for advanced metal-oxide-semiconductor field effect transistors (MOSFETs) because of its high mobility. Reducing interface trap density (Dit) and forming high quality high-k/Ge gate stacks are required for high-performance Ge-MOSFET. The GeO2 interfacial layer (IL) between high-k and Ge is considered as one of the best solutions to improve the interface quality. Therefore, in this study, various passivation ways including thermal oxidation, ozone oxidation and modified ozone oxidation were investigated. The impacts of three oxygen-related passivation methods on interface modification, gate leakage suppression, and dielectric enhancement were discussed.

Schottky barrier height modulation in metal/N-Ge system

Fermi level pinning at the Ge valence band results in a high Schottky barrier height (SBH) for all metal/n-Ge contacts. In this work, by inserting an ultrathin insulator between metal and germanium, the SBH of Al/Ge can be reduced from 0.6 eV to about 0.3 eV. Barrier height reduction was measured and compared for several inserted insulators. This structure has application as a low resistance ohmic contact for Ge nMOSFETs.

Decoupling between rare-earth moment and transition metal moment in NdCo12-xVx compounds

Single-phase compounds NdCo12−xVx (x=2.2–2.6) crystallizing in the tetragonal ThMn12 structure with space group I4/mmm are synthesized. The lattice parameters a and c increase linearly with increasing V content. The Curie temperature of the compounds shows a linear decrease from 309 K for x=2.2 to 147 K for x=2.6. A domain-wall pinning phenomenon is observed in all of the compounds. It is intriguing that the Nd ions seem to make no contribution to the total moment of the compounds in an applied magnetic field up to 50 kOe. A further increase of the applied field induces a moment of a Nd sublattice that ferromagnetically couples with the moment of a Co sublattice. The instability of the Nd moment in NdCo12−xVx compounds can be well understood by the local environment effect.