HEAVILY ZN-DOPED GRADED-BASE ALGAAS/GEAS HBTS GROWN BY MOCVD

Heavily Zn-doped graded-base AlGaAs/GaAs HBT's, which had base doping concentrations of 3.5 x 10(19), 5.5 x 10(19), and 8.1 x 10(19) cm-3, were fabricated using MOCVD-grown epitaxial wafers. The maximum measured current gain was 42 with the base doping concentration of as high as 8.1 x 10(19) cm-3. The current gain decreased drastically from 96 to 42 when doping concentration increased from 3.5 x 10(19) to 8.1 x 10(19) cm-3. Assuming that the emitter efficiency is unity, the minority electron lifetime in the base is estimated by the current gain by consideration of drift in the graded base. The dependence of the electron lifetime in the graded base on Zn doping concentration was similar to that in the uniform base reported in a previous paper.