This invention relates to gate turn-off diodes for power switching applications, particularly but not exclusively at high-frequency, and further relates to arrangements including such diodes.
Gate turn-off diodes and their advantages are described in the article entitled "A Field Terminated Diode" by D. E. Houston et al. In I.E.E.E. Transactions on Electron Devices, Vol ED-23, No. 8, August 1976, pages 905 to 911. These diodes, which are for power switching applications, comprise a gate turn-off diode for power switching applications comprising a semiconductor body having opposite first and second major surfaces, and comprising an n-type cathode region, a p-type anode region, a higher resistivity base region of one conductivity type through which a main current path extends between the cathode and anode regions, the base region having a conductivity type determining dopant concentration of at most 5.times.10.sup.14 atoms per c.c. and forming a first p-n junction with one of the cathode and anode regions, a gate region which is of opposite conductivity type to the base region and forms with the base region a second p-n junction adjacent the main current path, and a gate electrode connected to the gate region for permitting this second p-n junction to be biased so as to permit interruption of said current path by a depletion layer extending from the biased second p-n junction. As described in said publication, the cathode region of these known devices adjoins one major surface of the body and is separated by the base region from the anode region which adjoins the opposite major surface; the gate region is in the form of a grid of stripes buried in the base region and extending parallel to the major surfaces.
Such known gate turn-off diodes are not easy to manufacture, particularly as regards the buried grid. It is not easy to obtain a low series resistance along the length of the grid stripes between the gate electrode and the active area of the device; too high a value for this resistance reduces the biasing of the second p-n junction along the length of the stripes and reduces the amount of current which can be carried by the grid. Furthermore, when the diode has been turned off by a sufficiently large gate voltage, this grid resistance can result in the device being turned on again by increasing the anode voltage; this can result in the diode being quite easily turned on again by a surge in the anode voltage.