A heterojunction bipolar transistor (HBT) may include an n-type doped crystalline collector formed in an upper portion of a crystalline silicon substrate layer; a p-type doped crystalline p+Si1-xGex layer, formed above the n-type doped collector, that forms a p-type doped internal base of the HBT; a crystalline silicon cap formed on the p-type doped crystalline p+Si1-xGex layer, in which the crystalline silicon cap includes an n-type impurity and forms an n-type doped emitter of the HBT; and an n-type doped crystalline silicon emitter stack formed within an opening through an insulating layer to an upper surface of the crystalline silicon cap.