Fabrication methods and device structures for a heterojunction bipolar transistor. A trench isolation region is formed that surrounds an active region of semiconductor material, a collector is formed in the active region, and a base layer is deposited that includes a first section over the trench isolation region, a second section over the active region, and a third section over the active region that connects the first section and the second section. An emitter is arranged over the second section of the base layer, and an extrinsic base layer is arranged over the first section of the base layer and the third section of the base layer. The extrinsic base layer includes a first section containing polycrystalline semiconductor material and a second section containing single-crystal semiconductor material. The first and second sections of the extrinsic base layer intersect along an interface that extends over the trench isolation region.

The methods of manufacture of GeSiSn heterojunction bipolar transistors, which include light emitting transistors and transistor lasers and photo-transistors and their related structures are described herein. Other embodiments are also disclosed herein.

This hetero-junction bipolar transistor includes a first n-type GaN layer, an Al.sub.xGa.sub.1-xN layer (0.1x0.5), an undoped GaN layer having a thickness of not less than 20 nm, a Mg-doped p-type GaN layer having a thickness of not less than 100 nm, and a second n-type GaN layer which are sequentially stacked. The first n-type GaN layer and the Al.sub.xGa.sub.1-xN layer form an emitter, the undoped GaN layer and the p-type GaN layer form a base, and the second n-type GaN layer forms a collector. During non-operation, two-dimensional hole gas is formed in a part of the undoped GaN layer near the hetero interface between the Al.sub.xGa.sub.1-xN layer and the undoped GaN layer. When the thickness of the p-type GaN layer is b [nm], the hole concentration of the p-type GaN layer is p [cm.sup.3], and the concentration of the two-dimensional hole gas is P.sub.s [cm.sup.2], pb10.sup.7+P.sub.s110.sup.13 [cm.sup.2] is satisfied.

This hetero-junction bipolar transistor includes a first n-type GaN layer, an Al.sub.xGa.sub.1-xN layer (0.1x0.5), an undoped GaN layer having a thickness of not less than 20 nm, a Mg-doped p-type GaN layer having a thickness of not less than 100 nm, and a second n-type GaN layer which are sequentially stacked. The first n-type GaN layer and the Al.sub.xGa.sub.1-xN layer form an emitter, the undoped GaN layer and the p-type GaN layer form a base, and the second n-type GaN layer forms a collector. During non-operation, two-dimensional hole gas is formed in a part of the undoped GaN layer near the hetero interface between the Al.sub.xGa.sub.1-xN layer and the undoped GaN layer. When the thickness of the p-type GaN layer is b [nm], the hole concentration of the p-type GaN layer is p [cm.sup.3], and the concentration of the two-dimensional hole gas is P.sub.s [cm.sup.2], pb10.sup.7+P.sub.s110.sup.13 [cm.sup.2] is satisfied.