Heterojunction bipolar transistor with inGaAs contact and etch stop layer for InP sub-collector

A heterojunction bipolar transistor (HBT), comprising:

• successive emitter, base and collector layers, and
• an InP sub-collector layer having an electrically insulative portion which electrically isolates the HBT.

A method of fabricating a heterojunction bipolar transistor, comprising:

• forming in succession an InP sub-collector layer, a thin electrically conductive InGaAs contact layer, and collector, base and emitter layers on a substrate, and
• etching said collector, base and emitter layers to a desired shape, using said contact layer as an etch stop to protect said sub-collector layer when the collector layer is etched.

A method of electrically isolating a bipolar transistor, comprising:

• forming said transistor with an InP sub-collector, and
• rendering a portion of said sub-collector electrically insulative to electrically isolate the transistor.