Simplified cross section of a <a href="https://en.wikipedia.org/wiki/planar_transistor" class="extiw" title="en:planar transistor">planar</a> <i>npn</i> Bipolar junction transistor showing the emitter, base and collector contacts and the respective regions with the silicon doping type.
Replacement SVG version of <a href="//commons.wikimedia.org/wiki/File:Npn_BJT_cross_section.PNG" title="File:Npn BJT cross section.PNG">File:Npn BJT cross section.PNG</a>
<a href="//commons.wikimedia.org/wiki/User:Matthewbeckler" title="User:Matthewbeckler">Matthewbeckler</a>
<span class="int-own-work" lang="en">Own work</span>