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High dose irradiation effects of gamma-rays up to 17 MGy (H2O) on 4H-SiC junction field effect transistors (JFETs) were investigated. Due to the irradiation, gradual positive threshold voltage (Vth) shift as high as 0.5 V and continuous decrease in transconductance gm were observed. In addition, Vth instability and hysteresis appeared for the irradiated JFETs when the gate voltage (VG) sweep direction, sweep interval, i.e., averaged sweeping rate, sweep range, and delay time were changed. Increase of VG interval attributed to positive Vth shift for both forward and reverse directions, whereas narrowing of sweep range and increase of delay time resulting in a more noticeable negative shift of Vth for the reverse direction. Such Vth hysteresis indicates that capture and release of carriers predominantly took place via hole traps formed around the gate region due to high dose gamma-ray irradiation. [ABSTRACT FROM AUTHOR]

Gamma-ray irradiation into vertical type n-channel hexagonal (4H)-silicon carbide (SiC) metal-oxide-semiconductor field effect transistors (MOSFETs) was performed under various gate biases. The threshold voltage for the MOSFETs irradiated with a constant positive gate bias showed a large negative shift, and the shift slightly recovered above 100 kGy. For MOSFETs with non- and a negative constant biases, no significant change in threshold voltage, Vth, was observed up to 400 kGy. By changing the gate bias from positive bias to either negative or non-bias, the Vth significantly recovered from the large negative voltage shift induced by 50 kGy irradiation with positive gate bias after only 10 kGy irradiation with either negative or zero bias. It indicates that the positive charges generated in the gate oxide near the oxide-SiC interface due to irradiation were removed or recombined instantly by the irradiation under zero or negative biases. [ABSTRACT FROM AUTHOR]

Silicon carbide (SiC) metal-oxide-semiconductor field effect transistors (MOSFETs) are expected as power electronic devices for high radiative conditions, including nuclear plants and space. Radiation response of commercial-grade prototype SiC MOSFETs with applying the gate bias is of interest, in terms of installation of the device in robots or sensors working under such radioactive circumstances. Due to gamma-rays irradiation, the threshold voltages (Vth) of samples with un- and negative-biased up to −4.5 V slightly shift toward the negative voltage side. In contrast, the positive bias of 2.25 V shifts Vth more negatively. Positive charge densities trapped in the gate oxide of un- and positive-biased samples increased with increasing dose. However, no significant increase was observed for negative-biased samples of −2.25 and −4.5 V. We calculated characteristic parameters for the accumulation of holes in the gate oxide, σpJp which is defined as the product of current density due to holes generated by irradiation and capture cross section for a hole in a trap, and it is lower for these negative biased samples compared with the unbiased case. Application of appropriate negative gate biases to SiC MOSFETs during irradiation suppresses accumulation of positive charges in the gate oxide and negative shift of Vth, due to irradiation. [ABSTRACT FROM AUTHOR]