High on-state breakdown heterojunction bipolar transistor

Abstract

A heterojunction bipolar transistor (HBT) is provided with an improved on-state breakdown voltage V CE. The improvement of the on-state breakdown voltage for the HBT improves the output power characteristics of the HBT and the ability of the HBT to withstand large impedance mismatch (large VSWR). The improvement in the on-state breakdown voltage is related to the suppression of high electric fields adjacent a junction of a collector layer and a sub-collector layer forming a collector region of the HBT.

1 . A heterojunction bipolar transistor, comprising
 a substrate;   a collector region having a plurality of layers formed of a first material and a layer of a second material;   a base region having at least one layer formed of said first material;   an emitter region having at least one layer formed of a third material; and   a contact region having a first layer formed of said first material and a second layer of a fourth material;   wherein the collector region reduces an electric field adjacent to two adjacent layers of the plurality of layers of said collector region to improve a drain-source on-state breakdown voltage of the heterojunction bipolar transistor.   
     
     
         2 . The heterojunction bipolar transistor of  claim 1 , wherein the first material comprises GaAs. 
     
     
         3 . The heterojunction bipolar transistor of  claim 1 , wherein the second material comprises AlGaAs. 
     
     
         4 . The heterojunction bipolar transistor of  claim 1 , wherein the third material comprises InGaP. 
     
     
         5 . The heterojunction bipolar transistor of  claim 1 , wherein the fourth material comprises In 0.5 Ga 0.5 As. 
     
     
         6 . The heterojunction bipolar transistor of  claim 1 , wherein the plurality of layers of the first material of the collector region comprises,
 a sub-collector layer of the first material;   a first collector layer of the first material; and   a second collector layer of the first material.   
     
     
         7 . The heterojunction bipolar transistor of  claim 6 , wherein the first collector layer of the first material has a thickness of between about 200 nm and about 400 nm. 
     
     
         8 . The heterojunction bipolar transistor of  claim 6 , wherein the second collector layer of the first material has a thickness of between about 200 nm and about 400 nm. 
     
     
         9 . The heterojunction bipolar transistor of  claim 6 , wherein the sub-collector layer has a thickness of between about 100 nm and about 500 nm. 
     
     
         10 . The heterojunction bipolar transistor of  claim 6 , wherein in the collector region the layer of the second material of has a thickness of about 200 nm. 
     
     
         11 . The heterojunction bipolar transistor of  claim 6 , wherein the substrate comprises a semi-insulating material. 
     
     
         12 . The heterojunction bipolar transistor of  claim 1 , wherein the layer of the second material has an impurity concentration different from one of the plurality of layers of the first material. 
     
     
         13 . A heterojunction bipolar transistor, comprising
 a substrate;   a collector region having a first layer formed of a first material and at least a second layer formed of the first material, the second layer having a gradually varied doping concentration from a first surface to a second surface of the second layer;   a base region having at least one layer formed of said first material;   an emitter region having at least one layer formed of a second material; and   a contact region having a first layer formed of said first material and a second layer formed of a third material;   wherein the collector region reduces an electric field adjacent to a first surface of the first layer of the first material and a first surface of the second layer of the first material to improve a drain source on-state breakdown voltage of the heterojunction bipolar transistor.   
     
     
         14 . The heterojunction bipolar transistor of  claim 13 , wherein the first material comprises GaAs. 
     
     
         15 . The heterojunction bipolar transistor of  claim 13 , wherein the doping concentration of the at least second layer of the first material forming a portion of the collector region increases in concentration from the first surface of the second layer adjacent a surface of the base region to the second surface of the second layer adjacent a first surface of the first layer of collector region. 
     
     
         16 . The heterojunction bipolar transistor of  claim 13 , wherein the first layer of the first material of the collector region comprises, a sub-collector layer of the first material. 
     
     
         17 . The heterojunction bipolar transistor of  claim 13 , wherein the second layer of the first material of the collector region comprises, a collector layer of the first material.