Power semiconductor devices with mesa structures and buffer layers including mesa steps

摘要

A bipolar junction transistor includes a collector having a first conductivity type, a drift layer having the first conductivity type on the collector, a base layer on the drift layer and having a second conductivity type opposite the first conductivity type, a lightly doped buffer layer having the first conductivity type on the base layer and forming a p-n junction with the base layer, and an emitter mesa having the first conductivity type on the buffer layer and having a sidewall. The buffer layer includes a mesa step adjacent to and spaced laterally apart from the sidewall of the emitter mesa, and a first thickness of the buffer layer beneath the emitter mesa is greater than a second thickness of the buffer layer outside the mesa step.