pHEMT and HBT integrated epitaxial structure

An improved pseudomorphic high electron mobility transistor (pHEMT) and heterojunction bipolar transistor (HBT) integrated epitaxial structure, comprising:

• a substrate;
• a pHEMT structure formed on said substrate;
• an etching-stop spacer layer formed on said pHEMT structure;
• and
• an HBT structure formed on said etching-stop spacer layer;
• wherein said pHEMT structure comprises:
• a buffer layer;
• a bottom barrier layer formed on said buffer layer;
• a first channel spacer layer formed on said bottom barrier layer;
• a channel layer formed on said first channel spacer layer, wherein said channel layer is composed of InxGa1-xAs compound semiconductor with the Indium content 0.2<x<0.5;
• a second channel spacer layer formed on said channel layer;
• a Schottky spacer layer formed on said second channel spacer layer;
• a Schottky donor layer formed on said Schottky spacer layer;
• a Schottky barrier layer formed on said Schottky donor layer;
• an etching-stop layer formed on said Schottky barrier layer;
• and
• at least one cap layer formed on said etching-stop layer;
• and wherein said HBT structure comprises:
• a sub-collector layer formed on said etching-stop spacer layer;
• a collector layer formed on said sub-collector layer;
• a base layer formed on said collector layer;
• an emitter layer formed on said base layer;
• and
• an emitter cap layer formed on said emitter layer.