| 摘要 |
The invention provides a heterojunction bipolar transistor comprising a substrate having a collector therein, an intrinsic base region, a first extrinsic base region, a second extrinsic base region, an emitter on the intrinsic base layer and a spacer adjacent the emitter and on the first extrinsic base region. The first extrinsic base region is adjacent the intrinsic base region and the second extrinsic base region is adjacent the first extrinsic base region on the substrate, wherein a dopant concentration of the second extrinsic base region is higher than a dopant concentration of the first extrinsic base region.
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