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ABSTRACT: The field of SiC electronics has progressed rapidly in recent years, but certain electronic properties remain poorly understood. For example, a consensus has not been reached as to the specific point defects which limit minority carrier recombination, and little is known about defects which limit generation lifetimes. This paper investigates generation lifetimes using the pulsed MOS capacitor technique and compares the results with defect densities, recombination lifetimes, and Schottky diode characteristics in the same material for the first time. Carrier generation lifetimes in 4H-SiC epilayers range from less than 1 ns to approximately 1 μs and depend strongly on measurement conditions and data interpretation. They are limited by dislocations only at densities higher than 10<sup>6</sup> cm<sup>-2</sup>.The only point defect that is theoretically capable of limiting generation lifetime to the levels currently observed in 4H-SiC is EH 6/7. However, this defect cannot account for the case where generation lifetimes are lower than recombination lifetimes in the same area. This is not seen in silicon and seems to be inconsistent with theory. Possible reasons for these perplexing results are discussed, and it is attempted to form a framework with which further understanding of the significance of carrier generation lifetime measurements in SiC can be achieved.
IEEE Transactions on Electron Devices 09/2010; · 2.32 Impact Factor
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ABSTRACT: A new method for precisely measuring low gate oxide currents by measuring the charge leaking through the oxide in a pulsed metal oxide semiconductor capacitor (MOS-C) is presented. Using basic equipment, it is possible to measure currents less than 10 fA/cm<sup>2</sup> . The relevant theory is developed to use these capacitance-time data to extract an approximate leakage current and the effect on the extracted generation lifetime. The technique is simple and requires the same equipment used for pulsed MOS-C generation lifetime measurements. Experimental results are presented, which are consistent with theory.
IEEE Transactions on Electron Devices 03/2008; · 2.32 Impact Factor
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ABSTRACT: Generation lifetimes and interface state densities of n -type 4H -SiC metal oxide semiconductor (MOS) capacitors are characterized by using the pulsed MOS capacitor technique. A decrease in lifetime and increase in interface state density occurs when the devices are negatively biased at 400 ° C . This behavior is consistent with an effect seen in Si / Si O <sub>2</sub> devices known as negative bias temperature instability. A portion of the lifetime degradation caused by this effect can be recovered by removing the negative bias as well as by positively biasing the device.
Applied Physics Letters 07/2007; · 3.84 Impact Factor
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ABSTRACT: 1. Abstract Compared to silicon, there have been relatively few comparative studies of recombination and carrier lifetimes in SiC. For the first time, both generation and recombination carrier lifetimes are reported from the same areas in 20 µm thick 4H SiC n-/n+ epi-wafer structures. The ratio of the generation to recombination lifetime is much different in SiC compared to Si. Activation energy calculated from SiC generation lifetimes shows that traps with energy levels near mid-gap dominate the generation lifetime. Comparison of both generation and recombination lifetimes and dislocation counts measured in the device area show no correlation in either case. 2. Introduction Carrier lifetime is an established method for characterizing semiconductor materials. Both carrier recombination and generation lifetimes provide important and complementary information to understand electrical defects in the material and the AC operation of semiconductor devices. Carrier lifetime testing and mapping is well established in silicon technology for grading material quality [1]. To achieve high-temperature high-power and fast switching bipolar SiC devices, information on the complete recombination and generation process is important to fully assess the material performance. In this paper both generation and recombination lifetimes, measured by pulsed MOS-capacitor (MOS-C) and photoluminescence (PL) spectroscopy, respectively, are measured at identical device locations for direct comparison and correlation between lifetime values and material defects.
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ABSTRACT: Small bursts of inversion layer charge in 4H-SiC metal oxide semiconductor capacitors leak through the oxide layer leading to discontinuities during capacitance-time measurements. This behavior has been observed using non-equilibrium capacitance-time (C-t) and current-time (I-t) measurements, at room temperature and at 400degC.
Reliability Physics Symposium, 2008. IRPS 2008. IEEE International;
