Showing papers by "Marko J. Tadjer published in 2008"

Temperature and Time Dependent Threshold Voltage Instability in 4H-SiC Power DMOSFET Devices

Abstract: Threshold voltage (Vth) was measured on 4H-SiC power DMOSFET devices as a function of temperature, gate stress, and gate stress time. Vth varied linearly with gate stress and gate stress time and inversely with temperature. This instability is explained with the trapping rate of channel electrons at or near the SiO2-SiC interface. Since the measurement scale of Vth is large in this case (it takes approx. 20 s to measure Vth), it is assumed that fast interface traps, i.e., ones closer to the interface, are already filled and do not contribute to the shift in Vth. Comparison with theoretical calculations shows the rate of carrier detrapping becomes higher with temperature and as a result the measured value of Vth approaches the theoretical value.

Temperature Dependence of Shockley Stacking Fault Expansion and Contraction in 4H-SiC p-i-n Diodes

Abstract: The nucleation and expansion of Shockley stacking faults (SSFs) in 4H-SiC is known to induce an increase in the forward voltage drop (Vf) of bipolar devices such as pin diodes. However, recent annealing experiments have shown that SSFs can not only expand, but that low temperature annealing (210-7000C) induces a contraction of the SSFs that is coupled with a full and repeatable recovery of the Vf drift. Here we report that following extended periods of forward bias operation that the Vf drift of 10kV 4H-SiC pin diodes saturates, with the saturation Vf drift dropping with increasing stressing temperature. Upon reaching saturation, increases in temperature during forward bias operation at the same injection conditions also lead to a partial recovery of the Vf drift. Furthermore, the magnitude of this current-induced recovery is dependent upon the injection current, as reductions in the current cause a slower, but larger overall Vf drift recovery. All of these results clearly indicate that the current driving force models for SSF expansion are either incomplete or incorrect and that further efforts are required for a more complete understanding of SSF dynamics to be obtained.

Influence of Shockley Stacking Fault Expansion and Contraction on the Electrical Behavior of 4H-SiC DMOSFETs and MPS diodes

Abstract: The forward voltage drop (Vf) increase observed in 4H-SiC bipolar devices such as pin diodes due to recombination-induced Shockley stacking fault (SSF) creation and expansion has been widely discussed in the literature. It was long believed that the deleterious affect of these defects was limited to bipolar devices. However, it was recently reported that forward biasing of the body diode of a 10kV 4H-SiC DMOSFET led to similar Vf increases in the body diode I-V curve as well as a corresponding degradation in the majority carrier conduction characteristics as well and this degradation was believed to be due to the creation and expansion of SSFs during the body diode forward biasing. Here we report measurements comparing the influence of similar stressing, along with annealing and current-induced recovery experiments in DMOSFETs and merged pin-Schottky diodes with the previously reported results of these experiments in 4H-SiC pin diodes. The results of these experiments provide sufficient support that the observed degradation in the majority carrier conduction characteristics is the result of SSF expansion.