| 摘要 |
One of the aspects of the present invention is to provide a semiconductor device, which includes a semiconductor layer of a first conductive type having first and second surfaces. The semiconductor layer includes a base region of a second conductive type formed in the first surface and an emitter region of the first conductive type formed in the base region. Also, the semiconductor device includes a buffer layer of the first conductive type formed on the second surface of the semiconductor layer, and a collector layer of the second conductive type formed on the buffer layer. The buffer layer has a maximal concentration of the first conductive type impurity therein of approximately 5x10<SUP>15 cm</SUP><SUP>-3 </SUP>or less, and the collector layer has a maximal concentration of the second conductive type impurity therein of approximately 1x10<SUP>17 cm</SUP><SUP>-3 </SUP>or more. Further, the ratio of the maximal concentration of the collector layer to the maximal concentration of the buffer layer being greater than 100. The collector layer has a thickness of approximately 1 mum or less.
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