On the design of base-collector junction of InGaAs/InP DHBT

The effects of the composite-collector structure and the δ-doping density in InGaAs/InP DHBT on the Kirk current have been studied. The effective grade layer in the discretely graded layer goes into the InGaAs setback layer. The formulas of the maximum doping density, the maximum Kirk current, and the corresponding δ-doping density are derived under different Kirk-effect conditions. Both the maximum collector doping density and the maximum Kirk current are dependent on the δ-doping layer. By optimizing the delta doping, the Kirk current density can be greatly increased. Supported by the National Basic Research Program of China (“973”) (Grant No. 2002CB311902)