Materials Science Forum Vol. 924

Abstract: In this work, >2kV PiN diodes with >10um deep implant of B⁺ and 6um deep implant of Al⁺ have been fabricated to evaluate the quality of resulting pn junction after high-energy implantation. Acceptable low leakage currents at reverse bias and stable avalanche breakdown were observed for high energy implanted diodes (HEI-diodes) when compared to No-HEI-diodes that suggests minimal defect sites present after activation anneal.

Abstract: This paper presents OBIC measurements performed at near breakdown voltage on two devices with different JTE doses. Overcurrent has been measured either at the JTE periphery or at the P⁺ border. Such overcurrent is present due to the electric field enhancement near the breakdown voltage. This hypothesis is proved by the electroluminescence. TCAD simulation of two different JTE doses yielded similar results to the OBIC measurements.

Abstract: Reliability characterization of SiC devices is an ongoing activity. For this work, 650 V SiC JBS diodes in TO247 housings were tested in H3TRB. After a test period of 4000 hours none of the devices had failed during the test and only two out of sixteen devices had failed during blocking curve measurements performed at intermediate time steps. This is significantly better performance than many silicon devices offer today. The failure spots of the failed devices were detected at the edge of the main junction appearing as semi-circular cavities in the aluminum metallization. All other devices did not even show deviations from their original blocking curves.

Abstract: A state-of-the art family of 1200 V junction barrier Schottky (JBS) diodes was developed. These devices are highly competitive in switching applications thanks to low specific series resistance (1.8 mΩ.cm² at current rating) and low capacitive charge (1420 nC.cm^-2 at 800 V). A uniform avalanche distribution over the active area combined with an optimized high-voltage termination provides industry-leading UIS capabilities. Stringent reliability tests were performed to meet the qualification requirements for the industrial market.

Abstract: Temperature-dependent mechanisms and characteristics of 4H-SiC JBS rectifiers were described by theoretical and experimental results. The forward on-resistance of 4H-SiC JBS rectifier consists of several components, the drift region resistance is most sensitive to temperature than others. Comparing theoretical results with experimental data indicates that the leakage current is mainly affected by the thermionic emission, the image force barrier height lowering and tunneling. At different temperatures and reverse bias, the contribution of barrier lowering and the tunneling to leakage current is not the same. The temperature of critical point decreases with the increasing of the concentration of N_D or the reverse bias voltage V_R. Samples with the doping concentration of N_D=6.5E15cm^-3 and N_D=1E16cm^-3 were manufactured in the same process. The forward I–V-T and reverse I–V-T characteristics of the JBS samples were measured at different temperatures (300K to 523K), and temperature-dependent ideality factor, barrier height and resistance were also analyzed, which are in good agreement with simulation results.

Abstract: In this paper we will present the results of repetitive surge stress carried out on six 3.3 kV-5A Ti/Ni 4H-SiC JBS diodes. Repetitive current peaks between 10 A and 24 A have been applied and some diodes were able to endure 100,000 cycles while others failed before. The causes of failure have not been determined but a correlation between peak surge current and physical parameters evolution rate has been proven. Simulations show that contact temperature during surge can reach 300 °C, which is very close to Schottky contact annealing temperatures.

Abstract: This paper presents an investigation into the performance of SiC JBS diodes rated for 6.5kV applications. For the active area layout, two hexagonal cell designs with different A_Schottky/A_Total ratios have been considered. For completeness, the JBS performance is compared to that of SiC PiN diodes, fabricated on the same wafer. A benchmark against state of the art PiN diodes in Si technology is also provided.

Abstract: The reverse-bias current-voltage characteristics of commercial 1200 V 4H-silicon-carbide junction barrier Schottky (SiC-JBS) rectifiers are studied both experimentally and through numerical simulation. The reverse leakage current measured from physical devices is observed to display both a strong temperature and field dependence. A model is presented to explain the observed behavior based on a combination of trap-assisted tunneling and a thermionic-emission mechanism through a potential barrier located at the metal-SiC interface. The study shows that a two-level trapping model can be necessary to properly explain the measured data. Excellent agreement between the models and the measurements is obtained over a wide range of bias and temperature.

Abstract: Electron irradiation of high voltage Ni/4H-SiC Schottky diodes with the dose Φ=(0.2-7)×10¹⁶cm^-2 led to increase in the base resistance, appearance of slow relaxation processes at extremely small currents, and increase of the low frequency noise. On exponential part of the current-voltage characteristics and on linear part of current-voltage characteristics in non-irradiated samples, low frequency noise always has the form of the 1/f noise. On linear part of the current-voltage characteristics in irradiated diodes the generation recombination (GR) noise predominates. Temperature dependences of the base resistivity and character of GR noise indicate that mainly Z_1/2 center contributes to the change in the parameters of irradiated samples. Capture cross section of this level, obtained from noise measurements, is within the range (8×10^-16-2×10^-15) cm² and only weakly depends on temperature.

Abstract: We report on the development of a new generation of SiC Schottky rectifier devices employing a Molybdenum based barrier metal system and a new stripe cell design for field shielding and optimized area utilization. The Schottky barrier height is reduced and thus the conduction losses are decreased significantly. The balance between forward conduction and reverse leakage losses as well as the homogeneity and stability of the new barrier system are investigated carefully.