Heterojunction bipolar transistor

A heterojunction bipolar transistor, comprising a plurality of semiconductor layers epitaxially grown on a GaAs substrate and forming a collector over the GaAs substrate, a base on the collector, and an emitter on the base, wherein the base comprises:

• a first base layer comprising InmGa1-mAs with an Indium content m being in the range 0<m<1, and
• a second base layer inserted between the second base layer and the emitter and comprising InnGa1-nAs with an Indium content n being in the range 0<n<1,
• wherein an average Indium content n of the second base layer is larger than the Indium content m of the first base layer at a second base layer side inside the first base layer,
• wherein the first base layer and the second base layer are pseudomorphic epitaxial layers with compressive strains due to the lattice mismatch to the GaAs substrate,
• wherein the heterojunction bipolar transistor is an npn-type bipolar transistor, and
• wherein the first base layer and the second base layer have p-type conductivity.

A heterojunction bipolar transistor, comprising a plurality of semiconductor layers epitaxially grown on a GaAs substrate and forming a collector over the GaAs substrate, a base on the collector, and an emitter on the base,

• wherein the base comprises a first base layer which is pseudomorphic to GaAs with a first bulk lattice constant being at least 0.15% larger than the bulk lattice constant of GaAs,
• wherein the emitter comprises a first emitter layer which is pseudomorphic to GaAs with a second bulk lattice constant being at least 0.15% smaller than the bulk lattice constant of GaAs,
• wherein the first base layer is a pseudomorphic epitaxial layer with a compressive strain due to the lattice mismatch to the GaAs substrate,
• wherein the first emitter layer is a pseudomorphic epitaxial layer with a tensile strain due to the lattice mismatch to the GaAs substrate,
• wherein the heterojunction bipolar transistor is an npn-type bipolar transistor,
• wherein the first base layer has p-type conductivity, and
• wherein the first emitter layer has n-type conductivity.