Switching rate and power capacity improvement of semiconductor power device by effect of magnetic fields

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The influence of magnetic fields on carrier behavior in power semiconductor devices was examined in order to obtain technical data required for designing devices that can switch in high-current density region with high di/dt characteristics for pulsed power applications. Free carrier absorption method using the infrared probe laser with wavelength of 1.55μm was employed to measure spatial and temporal change in carrier distribution of a pin-diode, which has a basic structure of power semiconductor devices. The probe laser beam ray was analyzed and spatial resolution of 40μm was obtained. Spatial nonuniformity of the carrier density caused by Lorentz force was successfully observed. The factor contributed to the increase of on-resistance by the magnetic field was discussed. The spatial nonuniformity of the carrier density distribution led to the decrease of the effective cross section of the current in the device. As actually utilized power device, a SI-thyristor, which attracted much attention as a possible candidate for a fast switching device in pulsed power technology, was adopted to examine the carrier behavior. The carrier in the semiconductor power devices works to remove the potential barrier and to transfer electric charges from the anode to the cathode. The amount of carrier involved in transferring the electric charge was comparatively small for the fast pulse switching, even if the current density was considerably high. In this research, the possibility of improving the turn-off characteristics and establishing high-repetition operation of the SI-thyristor was confirmed.