| 摘要 |
PURPOSE: To provide an HTB which is thermally stable at a high voltage wherein unstableness is liable to be generated under usual operating conditions. CONSTITUTION: An HTB having an N-type collector layer 13, a P-type base layer 14 and an N-type emitter layer 20 is doped with impurities of concentration lager than or equal to 2×10<18> cm<-3> . An N-type impurity layer 15 which is perfectly turned into a depletion layer when it is biased in the usual operation is formed on an interface with the P-type base layer 14 in the N-type emitter layer 20. The P-type base layer 14 has electron affinity larger than the N-type emitter layer 20 and has impurity concentration higher than the N-type impurity layer 15.
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