| 摘要 |
PURPOSE:To make the gradient of an electric field gentle and to improve the breakdown strength by selecting the impurity concentrations and thicknesses of the first, third layers so that an electric field by a depleted layer extending from the P-N junction formed by first and third semiconductor layers exists largely in the first layer and that the depleted layer reaches a second semiconductor layer. CONSTITUTION:An N<-> type layer 21 is reduced in its sectional area from a P-N junction toward an N<+> type substrate 1, an N<--> layer 22 is formed instead. When a low potential is applied to an electrode 7 and a high potential is applied to an electrode 8, a depleted layer from a P-N junction formed with a P<+> type layer 3 and the layer 21 is extended in the layer 21 as the applied voltage is raised to reach the substrate 1. That is, the shape of the depleted layer is also formed in a shape similar to that of the layer 21. Since the layer 3 has a high impurity concentration, the depleted layer is not almost extended to the side of the layer 3. The layer 21 is reduced in its sectional area from the layer 3 toward the substrate 1. If the electrode 7 and a gate electrode 6 are set to a low potential and the drain electrode 8 is set to a high potential, i.e., in an OFF state, it can be supported by the layer 21 thinner than the layer 2. Thus, when the electrode 6 is a high potential, i.e., in an ON state, its resistance is reduced. |
