Improved high frequency performance by composite emitter AlGaAs/GaInP heterojunction bipolar transistors fabricated using chemical beam epitaxy

A new emitter design based on composite AlGaAs/GaInP approach is described which allows significant reduction of C/sub BE/ and improved high frequency performance. Self-aligned composite AlGaAs/GaInP and traditional emitter design HBTs were fabricated on CBE layers grown with TBA/TBP precursors. C/sub BE/ of composite emitter HBTs is significantly lower than for traditional designs and does not show significant variation with collector current. This leads to enhanced f/sub /spl tau// characteristics for composite emitter HBT designs and confirms the theoretical expectations. The C/sub BE/ achieved with the new designs was by at least 4 times lower than that of conventional transistors and resulted in 20% enhancement of cutoff frequency.