Jia Renxu

Effect of re-oxidation annealing process on the SiO2/SiC interface characteristics

The effect of the different re-oxidation annealing (ROA) processes on the SiO2/SiC interface characteristics has been investigated. With different annealing processes, the flat band voltage, effective dielectric charge density and interface trap density are obtained from the capacitance—voltage curves. It is found that the lowest interface trap density is obtained by the wet-oxidation annealing process at 1050 °C for 30 min, while a large number of effective dielectric charges are generated. The components at the SiO2/SiC interface are analyzed by X-ray photoelectron spectroscopy (XPS) testing. It is found that the effective dielectric charges are generated due to the existence of the C and H atoms in the wet-oxidation annealing process.

Investigation of a 4H—SiC metal—insulation—semiconductor structure with an Al2O3/SiO2 stacked dielectric

Atomic layer deposited (ALD) Al2O3/dry-oxidized ultrathin SiO2 films as a high-k gate dielectric grown on 8° off-axis 4H—SiC (0001) epitaxial wafers are investigated in this paper. The metal—insulation—semiconductor (MIS) capacitors, respectively with different gate dielectric stacks (Al2O3/SiO2, Al2O3, and SiO2) are fabricated and compared with each other. The I—V measurements show that the Al2O3/SiO2 stack has a high breakdown field (≥12 MV/cm) comparable to SiO2, and a relatively low gate leakage current of 1 × 10−7 A/cm2 at an electric field of 4 MV/cm comparable to Al2O3. The 1-MHz high frequency C—V measurements exhibit that the Al2O3/SiO2 stack has a smaller positive flat-band voltage shift and hysteresis voltage, indicating a less effective charge and slow-trap density near the interface.

Periodic solitons in dispersion decreasing fibers with a cosine profile

Periodic solitons are studied in dispersion decreasing fibers with a cosine profile. The variable-coefficient nonlinear Schrodinger equation, which can be used to describe the propagation of solitons, is investigated analytically. Analytic soliton solutions for this equation are derived with the Hirotas bilinear method. Using the soliton solutions, we obtain periodic solitons, and analyze the soliton characteristics. Influences of physical parameters on periodic solitons are discussed. The presented results can be used in optical communication systems and fiber lasers.

Deep level defects in unintentionally doped 4H-SiC homoepitaxial layer ∗

Unintentionally doped 4H-SiC homoepitaxial layers grown by hot-wall chemical vapor deposition (HWCVD) have been studied using photoluminescence (PL) technique in the temperature range of 10 to 240 K. A broadband green luminescence has been observed. Vacancies of carbon (VC) are revealed by electron spin resonance (ESR) technique at 110 K. The results strongly suggest that the green band luminescence, as shallow donor-deep accepter emission, is attributed to the vacancies of C and the extended defects. The broadband green luminescence spectrum can be fitted by the two Gauss-type spectra using nonlinear optimization technique. It shows that the broad- band green luminescence originates from the combination of two independent radiative transitions. The centers of two energy levels are located 2.378 and 2.130 eV below the conduction band, respectively, and the ends of two energy levels are expanded and superimposed each other.

First-principle calculation on the defect energy level of carbon vacancy in 4H–SiC

First, electronic structures of perfect wurtzite 4H{SiC were calculated by using rst-principle ultra-soft pseudopotential approach of the plane wave based on the density functional theory; and the structure changes, band structures, and density of states were studied. Then the defect energy level of carbon vacancy in band gap was examined by substituting the carbon in 4H{SiC with carbon vacancy. The calculated results indicate the new defect energy level generated by the carbon vacancy, and its location in the band gap in 4H{SiC, which has the character of deep acceptor. A proper explanation for green luminescence in 4H{SiC is given according to the calculated results which are in good agreement with our measurement results.

Energy-band alignment of atomic layer deposited（HfO2）x（Al2O3）1-x gate dielectrics on 4H-SiC

We study a series of (HfO2)x(Al2O3)1 − x /4H-SiC MOS capacitors. It is shown that the conduction band offset of HfO2 is 0.5 eV and the conduction band offset of HfAlO is 1.11–1.72 eV. The conduction band offsets of (HfO2)x(Al2O3)1 − x are increased with the increase of the Al composition, and the (HfO2)x(Al2O3)1 − x offer acceptable barrier heights (> 1 eV) for both electrons and holes. With a higher conduction band offset, (HfO2)x(Al2O3)1 − x/4H-SiC MOS capacitors result in a ~ 3 orders of magnitude lower gate leakage current at an effective electric field of 15 MV/cm and roughly the same effective breakdown field of ~ 25 MV/cm compared to HfO2. Considering the tradeoff among the band gap, the band offset, and the dielectric constant, we conclude that the optimum Al2O3 concentration is about 30% for an alternative gate dielectric in 4H-SiC power MOS-based transistors.

Robust Generation of Three-Particle W State with Atoms Trapped in Separate Cavities

This paper presents a scheme for generating three-particle W state of remote atoms trapped in leaky cavities. The scheme uses cavity decay to inject photons into a setup of optical devices which consist of a series of beam splitters and photon detectors. Photon detection on the output mode projects the atomic state into the W state. In the condition of ?weakly driven approach, it shows that the scheme is robust and has high fidelity. It also points out that the scheme is scalable to generate multi-atomic W state.