Materials Science Forum Vols. 600-603

Abstract: Hybrid SiC pulsed-power switch (having bipolar transistor structure) with 5 kV breakdown voltage and 1 kA peak current rating has been designed, which can be triggered optically using a GaAs or SiC front-end triggering structure with a rise time < 20 ns and for sub-microsecond pulse-widths. Structural details and physics-based simulation results are presented. It is shown, that GaAs triggering structure reduces the optical-triggering power requirement significantly without sacrificing switching speed as compared to a SiC optical-triggering structure.

Abstract: This paper reports on initial results from the first device tested of a “second generation” Pt-SiC Schottky diode hydrogen gas sensor that: 1) resides on the top of atomically flat 4H-SiC webbed cantilevers, 2) has integrated heater resistor, and 3) is bonded and packaged. With proper selection of heater resistor and sensor diode biases, rapid detection of H2 down to concentrations of 20 ppm was achieved. A stable sensor current gain of 125 ± 11 standard deviation was demonstrated during 250 hours of cyclic test exposures to 0.5% H2 and N2/air.

Abstract: This paper reports a 4H-SiC single photo avalanche diode (SPAD) operating at the solar blind wavelength of 280 nm. The SPAD has an avalanche breakdown voltage of 114V. At 90% and 95% of the breakdown voltage, the SPAD shows a low dark current of 57.2fA and 159fA, respectively. The quantum efficiency of 29.8% at 280nm and <0.007% at 400nm indicates a high UV-to-visible rejection ratio of >4300. Single photon counting measurement at 280nm shows that a single photon detection efficiency of 2.83% with a low dark count rate of 22kHz is achieved at the avalanche breakdown voltage of 116.8V.

Abstract: The hole dominated avalanche multiplication characteristics of 4H-SiC Separate Absorption and Multiplication avalanche photodiodes (SAM-APDs) were determined experimentally and modeled using a local multiplication model. The 0.5x 0.5mm2 diodes had very low dark current and exhibited sharp, uniform breakdown at about 580V. The data agree with modeling result using extrapolated impact ionization coefficients reported by Ng et al. and is probably valid for electric fields as low as ~0.9MV/cm at room temperature provided that both the C-V measurements and electric field determination in this work are correct. The packaged devices demonstrate a positive temperature coefficient of breakdown voltage for temperatures ranging from 100K to 300K which is a desired feature for extreme environment applications.

Abstract: In this work, we observed and investigated electro-luminescence (EL) from defects in 4H-SiC avalanche photodiodes. The EL irradiance originated from parallel lines oriented along the [11-20] crystallographic direction. Optical microscopy imaging was employed to analyze the intensity distribution of luminescencing lines at different current densities. Electron beam induced current (EBIC) methodology was employed to find correlation between the luminescencing defects and dislocations in the epi-layers. TEM analysis of the substrate region having the brightest luminescencing line was performed. There were a few defects at the depth of about 3 μm from the sample surface where EL intensity had the highest value.

Abstract: The Schottky barrier lowering in 4H-SiC interdigit Schottky-type UV photodiode is investigated in the presence of a thermally grown oxide layer on the exposed active area. Gain photocurrent is observed and correlated with the presence of the oxide and with the charge traps at the semiconductor/oxide interface. Photo-thermally stimulated current measurements evidenced that interface charge accumulation is optically promoted. Rise and fall photo-current measurements provided the time parameter of the trapping phenomenon.

Abstract: P+–n–n+-detector structures based on CVD films with an uncompensated donor concentration of 2×1014 cm-3 have been studied. The p+-region was created by implantation of Al ions. Preliminarily, the detectors were irradiated with 8 MeV protons at a fluence of 3×1014 cm-2 and then annealed in a vacuum at 600°C for 1 h and 700°C for 1 h. Nuclear spectrometric techniques with 5.4 MeV a-particles were employed to test the detectors. In measurements performed in the temperature range 20–150°C, the forward- and reverse-bias modes were compared. It is shown that the annealing leads to a higher collection efficiency of carriers generated by nuclear radiation and to a decrease in the amount of charge accumulated by traps in the course of testing. Despite the positive effect of the annealing, there remains a considerable amount of radiation defects, which is manifested, in particular, in the kinetics of the forward current.

Abstract: A compact SiC converter having power densities about 9 W/cm3 is designed and fabricated. It is confirmed that the converter operates in a thermally permissive range. The power loss of the module of the converter measured under motor operations is less than 50% of the similar-rating Si module loss. The shrink of the effective volume of DC-link capacitor is necessary to achieve the high power-density SiC converter, in addition to the decrease of the cooling system volume due to the loss reduction caused by SiC devices.

Abstract: Three dimensional models of both single-chip and multiple-chip power sub-modules were generated using ANSYS in order to simulate the effects of various substrate materials, heat fluxes, heat transfer coefficients, and device placement configurations on temperature and thermal stress contours. Alumina, aluminum-nitride, and CVD diamond were compared as substrates. Heat fluxes of 100 to 500 watts/cm2 resulted in SiC device junction temperatures in the range of 350 to 650 K. The predicted maximum operating temperature for a chip, to which 300 watts/cm2 of heat flux was applied, would be 239°C (512 K). In the applied heat flux range, the minimum and maximum Von Mises stress of a simulated single SiC device sub-module was between 1.2 MPa to 2.4 GPa. The maximum shear stress at 300 watts/cm2 was predicted to be 243 MPa. Both the maximum and minimum chip temperature decreased with increasing heat transfer coefficient from 25 to 2500 watts/m2 K. With modest cooling, represented by a heat transfer coefficient (hconv) of 250 watts/m2 K, SiC chips operated at 300 watts/cm2 power density maintained junction temperatures Tj < 400 K. If consistent with simulation results, CVD diamond integrated substrates should be superior to those comprised of AlN or Al2O3. Asymmetric device placement in the multi-chip module proved more effective at avoiding potential hot spots than the symmetric configuration.

Abstract: The new MOSFET-generation with SiC-materials seems well suited for power electronic converters up to 1200 V operating-voltage, and particularly for grid-feeding PhotoVoltaic-inverters, which transfer the DC power of the solar panel to the AC grid. Their high switching speed and low on-resistance RDS(on) allow the use of higher switching frequencies, which could mainly reduce the costs and weight of the converters. This paper shows a comparison between IGBT and SiC DMOSFET devices and first measurements of some 1200 V / 10 A SiC-DMOSFET samples made by CREE®.