Comparison of near-interface traps in Al2_2O3_3/4H-SiC and Al2_2O3_3/SiO2_2/4H-SiC structures

Aluminum oxide (Al2O3) has been grown by atomic layer deposition on n-type 4H-SiC with and without a thin silicon dioxide (SiO2) intermediate layer. By means of Capacitance Voltage and Thermal Dielectric Relaxation Current measurements, the interface properties have been investigated. Whereas for the samples with an interfacial SiO2 layer the highest near-interface trap density is found at 0.3 eV below the conduction band edge, Ec, the samples with only the Al2O3 dielectric exhibit a nearly trap free region close to Ec. For the Al2O3/SiC interface, the highest trap density appears between 0.4 to 0.6 eV below Ec. The results indicate the possibility for SiC-based MOSFETs with Al2O3 as the gate dielectric layer in future high performance devices.Comment: 3 figures. Applied Physics Letters, accepted for publicatio

Ion Implanted Phosphorous for 4H-SiC VDMOSFETs Source Regions: Effect of the Post Implantation Annealing Time

Van der Pauw devices have been fabricated by double ion implantation processes, namely P+ and Al+ co-implantation. Similarly to the source area in a SiC VD-MOSFET, a 5 × 1018 cm-3 P plateau is formed on the top of a buried 3 × 1018 cm-3 Al distribution for electrical isolation from the n- epilayer. The post implantation annealing temperature was 1600 °C. Annealing times equal to 30 min and 300 min have been compared. The increase of the annealing time produces both an increase of electron density as well as electron mobility. For comparison a HPSI 4H-SiC wafer, 1×1020 cm-3 P+ ion implanted and 1700 °C annealed for 30 min was also characterized.ISSN:0255-5476ISSN:1662-975

Preconception Health Knowledge among Undergraduate Women

Preconception health is a woman’s health before she becomes pregnant. It means knowing and understanding how preexisting health conditions and risk factors could affect a woman or her unborn child if she becomes pregnant (Office on Women’s Health, 2010). This study examined undergraduate students’ knowledge of recommended preconception health practices. A paper survey was distributed to general education classes in health, sociology, and family consumer science. This 33-item survey assessed demographics, barriers to practicing recommended preconception health behaviors, and knowledge of preconception health practices. Analyses included frequencies, independent t-test, and ANOVA. Respondents had a mean score of 42.85 (2.68) on the knowledge section of the survey; indicating that respondents had a high level of knowledge regarding preconception health practices and information. Respondents’ knowledge scores were statistically correlated with their preconception health practices and behaviors (r=.176, p=.000). As knowledge scores increased, preconception health practice and behaviors scores also increased. When analyzing participants’ current health behaviors as they relate to preconception health, it was found that most students are engaging in healthy behaviors

Simulation-Based Sensitivity Analysis of Conduction and Switching Losses for Silicon Carbide Power MOSFETs

The behavior of silicon carbide power MOSFETs is analyzed using TCAD device simulations with respect to conduction and switching losses. Device designs with varying breakdown voltages are simulated. The contributions to the on-state resistance are shown at room and elevated temperature. Whereas channel and substrate resistance dominate at low breakdown voltages, drift and JFET resistance dominate at high breakdown voltages. With increasing temperature, the channel resistance decreases and thus the drift resistance is the main contributor already at medium breakdown voltages. Manufacturing processes of a device can have a high influence on its losses. Variations in interface mobility, drift doping, and p-body doping can lead to a significant change of on-resistance, internal capacitances, and reverse recovery charge. For higher voltage classes the drift layer properties should be of major interest as it influences on-resistance and reverse recovery charge.ISSN:0255-5476ISSN:1662-975

Temperature Dependence of On-State Inter-Terminal Capacitances (C_gd and C_gs) of SiC MOSFETs and Frequency Limitations of their Measurements

Inter-terminal capacitances (ITCs) have major influence on the dynamic performance of power SiC MOSFETs. Knowledge of the exact values for the ITCs is required in order to perform accurate and predictive compact model simulations of their dynamic performance. Since commercial SiC MOSFETs are capable of operating in a wide range of temperatures, it is important to know the values of ITCs in the whole temperature range of operation. Direct measurements of the ITCs with standard equipment is possible only at low current levels (i.e. in the off-state (V_gs 0 V), however their values in the on-state (V_gs > V_th) also influence the MOSFETs switching performance. In this work, ITCs of a planar SiC MOSFET in the on-state are studied by the means of a calibrated TCAD model, revealing substantial temperature dependence in the range of 300-450 K. In the first approximation, this temperature dependence of the ITCs can be explained by a weaker temperature dependence of the MOSFET channel resistance in comparison to its JFET and epitaxial layer resistances. In addition, it is shown that at high frequencies stray inductances of the TO-247-3 package result in a change of the extracted values of the on-state ITCs. This effect is already notable at 1 MHz.ISSN:0255-5476ISSN:1662-975

Low-Energy Muons as a Tool for a Depth-Resolved Analysis of the SiO2/4H-SiC Interface

In this work, the potential of muon spin rotation (μSR) with low-energy muons (LE-μ) for the investigation of oxidation-induced defects at the SiO2/4H-SiC interface is explored. By using implantation energies for the muons in the keV range and comparing the fractions of muonium in different regions, the depth distribution of defects in the first 200 nm of the target material can be resolved. Defect profiles of interfaces with either deposited or thermally grown SiO2 layers on 4H-SiC are compared. The results show an increased number of defects in the case of a thermal oxide, both on the oxide and on the SiC side of the interface, with a spatial extension of a few tens of nm.ISSN:0255-5476ISSN:1662-975

First-principles study on electronic structure, phase stability, and optical properties of In2X2O7 (X= C, Si, Ge or Sn)

acceptedVersio