| 摘要 |
A transistor includes (a) a first semiconductor layer formed by a semiconductor substrate; (b) a second semiconductor layer formed on the first semiconductor layer and having an impurity of the same conductivity type as the first layer in a concentration lower than that of the first semiconductor layer; and (c) a third semiconductor layer formed on the second semiconductor layer having an impurity of the same conductivity type as the first semiconductor layer in a concentration lower than that of the second semiconductor layer. A base region is formed in the third layer and an emitter region is formed in the base region.
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