Base recombination of high performance InGaAs/InP HBT's

The authors have measured the gain of InGaAs HBTs (heterojunction bipolar transistors) as a function of base doping, with Zn and Be, using MOCVD (metal-organic chemical vapor deposition), and with C, using gas source MBE (molecular beam epitaxy), in the range of 5*10/sup 18/ to 8*10/sup 19/. Large area devices were measured at 2 kA/cm/sup 2/, where DC gain is saturated. Single HBTs, and double HBTs with graded base-collector junctions, were compared. Zn doping gave the highest figure of merit (HFE/R/sub bs//sup 2/), but the tendency for Zn to diffuse at high concentrations produced low collector breakdown voltage. Be doping resulted in high V/sub bc/>6 V at very low r/sub o/, <1000 Omega /sq, but lower gain. Published data indicate that this is not inherent with Be but may be related to the purity of the organometallic Be source used. Carbon-doped material fell in between these limits with more scatter in the data. Double heterojunction microwave power devices were fabricated from carbon doped material, using a dual self-aligned, dielectric assisted planarization process.