Collector layer structure for a double hetero-junction bipolar transistor for power amplification applications

Abstract

An indium phosphide based double hetero junction bipolar transistor with an increased collector-base breakdown voltage and a reduced operational knee voltage is provided by manipulating the conductivity in the collector region. The collector is formed using layers of different conductivities, with a region of the collector relatively close to the base being unintentionally or low doped. A voltage drop across the unintentionally doped region reduces the maximum value of the electric field and the velocity of carriers injected into the collector region at the base-collector junction. The conductivity throughout the collector region may be graded such that the highest conductivity occurs near the sub-collector and lowest conductivity occurs near the base region.

1 - 29 . (canceled)  
   
   
       30 . A method of decreasing a knee voltage and decreasing an electric field at a collector-base junction of a double heterojunction bipolar transistor, the method comprising: 
 providing a sub-collector above a semi-insulating indium phosphide (InP) substrate;    providing a first collector layer above the sub-collector, the first collector layer containing n-type InP;    providing a second collector layer above the first collector layer, the second conductor layer containing unintentionally doped InP and having a carrier concentration at most about one third of a maximum carrier concentration of the first collector layer;    providing a third collector layer above the second collector layer, the third layer containing n-type InP having a carrier concentration at least about ten times that of the second collector layer;    providing a base region above the collector that is substantially lattice-matched to the third collector layer, the base region having a smaller energy gap than the third collector layer;    providing an emitter above the base region; and    providing a cap above the emitter region.    
   
   
       31 . The method as recited in  claim 30 , wherein the first collector layer has substantially the same carrier concentration from an end closest to the sub-collector to an end most distal from the sub-collector.  
   
   
       32 . The method as recited in  claim 30 , further comprising providing a transitional material between the third collector layer and the base region, the transitional material having a carrier concentration less than about 5E16 cm −3 .  
   
   
       33 . A method of decreasing a knee voltage and decreasing an electric field at a collector-base junction of a double heterojunction bipolar transistor, the method comprising: 
 providing a sub-collector above a semi-insulating indium phosphide (InP) substrate;    providing an InP collector above the sub-collector, the collector having a region that is graded such that the region of the collector has a carrier concentration of at least about 1E17 cm −3  closest to the sub-collector and a carrier concentration of at most about 1E16 cm −3  most distal from the sub-collector;    providing a base region above the collector that is substantially lattice-matched to the collector, the base region having a smaller energy gap than the collector;    providing an emitter above the base region; and    providing a highly conductive cap above the emitter region.    
   
   
       34 . The method as recited in  claim 33 , further comprising providing a section of the collector nearest the base region that has a carrier concentration substantially higher than the carrier concentration of the region of the collector most distal from the sub-collector.  
   
   
       35 . The method as recited in  claim 34 , wherein the region of the collector is adjacent to the section of the collector.  
   
   
       36 . The method as recited in  claim 35 , wherein the carrier concentration is substantially uniformly graded from an end of the region of the collector closest to the sub-collector to an end of the region of the collector adjacent to the section of the collector.  
   
   
       37 . The method as recited in  claim 33 , wherein the region of the collector comprises a plurality of layers in which adjacent layers have decreasing carrier concentrations with increasing distance from the sub-collector.  
   
   
       38 . The method as recited in  claim 37 , wherein the carrier concentrations in each of the plurality of layers is substantially uniform.  
   
   
       39 . The method as recited in  claim 33 , further comprising providing an unintentionally doped transitional material between the collector and the base