Base recombination in high performance InGaAs/InP HBTs

MOCVD2f3, and with C, using gas source MBE4, in the range of 5x1Ol8 to 8 ~ 1 0 ~ ~ . Large area devices were measured at 2KA/cm2, where DC gain is saturated. Single hets, and double hets with graded base collector junctions, were compared, and various base-emitter doping setbacks were used to insure that neither emission nor collection efficiency influenced the results. For Zn and Be doped devices with the same base thickness, a log-log plot of DC gain( HFE) vs base sheet resistance (ro in R/sq) gives a line with a slope of 2. The trend is similar for C. Base emitter turn on voltages and ideality varied only slightly, indicating bulk recombination, not emitter efficiency, dominates gain. If we attribute this square law behavior to a CHHS Auger process, the estimated recombination constant ( 4'10-29 cm6/s) is actually slightly smaller than the optically derived value.5 Since all of our devices had Wb>500A where diffusive .transport. is expected6, HFE/(P'Wb )2 or equivalently HFE/ro2f appears to be a material related constant.