JPS6482563A - Semiconductor device - Google Patents

Abstract

PURPOSE:To shorten turn-off time wherein an internal electric field generates in a second region, and the effective diffusion constant of carrier in the second region is controlled, by making the impurity distribution in the second region have a gradient in the direction vertical to the main surface. CONSTITUTION:The concentration distribution of N-type impurity in a first N-type region 2 is minimum on the boundary surface between a first P-type region 1 and the region 2, increases in accordance with the approach to a second N-type region 3, and becomes medium on the boundary between the second N-type region 3 and the region 2. Since the concentration distribution of N-type impurity is made to have a gradient, an internal electric field generates in the first N-type region 2, and the direction of the field is inverse to the gradient of the N-type impurity concentration distribution. That is, the internal electric field acts so as to block the diffusion of positive hole which is injected from the first P-type region 1 and diffuses into the second N-type region 3. Therefore, the diffusion constant of positive hole and the base transit time are controlled by the internal electric field, and the turn-off time of IGBT is shorten.