| 摘要 |
PURPOSE:To correct the imbalance of a forward voltage drop value and a gate current value and thereby to increase a controllable current tolerance, by diffusing a heavy metal impurity or directing electron beams onto an NB layer corresponding to a projected plane on a cathode side of an NE layer formed on the fringe of a semiconductor substrate. CONSTITUTION:A heavy metal impurity, for example, a gold impurity is stuck by evaporation or other method on the surface of a PE layer corresponding to cathode segments 6a formed on the fringe of a semiconductor substrate 1 and then is diffused at 800-830deg. C or around for about 20 minutes. Nextly, a heavy metal impurity is stuck again by evaporation or other method on the whole surface of the PE layer and then is diffused at the lower temperature than before. As a substitute for sticking of a heavy metal impurity, electron beams may be directed onto the fringe of the semiconductor substrate stronger than onto the center of it. By this, the turn-off time of a cathode segment 6b formed on the center of the substrate and that of the cathode segments 6a formed on the fringe of the substrate can be uniformalized, and thereby, the imbalance of a forward voltage drop value and a gate current value is corrected and a controllable current tolerance is increased. |
