DCIV and spectral charge-pumping studies of γ-ray and X-ray irradiated power VDMOSFET devices

This paper reports the total dose effects and post-irradiation anneal effects on the two recombination current peaks and the bottom current in commercial power VDMOSFET devices irradiated with ¹³⁷Cs γ-ray or X-ray radiation. The two interface recombination current peaks show a slightly different rate of increase as a function of the radiation dose. Slightly different diode ideality factors are found in an n-channel device, 1.70 ± 0.10, 1.60 ± 0.10 and 1.20 ± 0.10 for the two DCIV current peaks and the bottom current, respectively. The saturation current of the gated diode, i.e., VDMOSFET, normalized by the input capacitance is shown to be a good parameter to monitor the interface state density. Spectral charge pumping data show that, of the above-midgap interface traps in an n-channel device, the energy below about E_i + 0.18 eV has a most significant increase in radiation-induced trap density and these traps may be responsible for the DCIV current peaks.