Ultra High Speed InP Heterojunction Bipolar Transistors

Abstract: This thesis deals with the development of high speed InPmesa HBT?s with power gain cut?off frequencies up toand above 300 GHz, with high current density and low collectordischarging times.Key developments are Pd?based base ohmics yielding basecontact resistances as low as 10 ?µm2, base?collector grades to enable to use ofInP in the collector, and an increase in the maximum currentdensity through collector design and thermal optimization.HBT?s with a linear doping gradient in the base are forthe first time reported and compared to HBT?s with abandgap graded base. The effect of degenerate base doping issimulated, as well as the base transit time.Key results include a DHBT with a 215 nm thick collector andan f?= 280GHz, and fmax=400 GHz. This represents the highest fmaxreported for a mesa HBT. Results also include aDHBT with a 150 nm thick collector and an f?= 300 GHz, and fmax=280 GHz. The maximum operating current densityhas been increased to above 10 mAµm while maintaining f?and fmax? 200 GHz.A mesa DHBT process with and as much yield and simplicity aspossible has been developed, while maintaining or pushingworld?class performance.