Improved emitter transit time using AlGaAs-GaInP composite emitter in GaInP/GaAs heterojunction bipolar transistors

A new emitter structure based on composite graded AlGaAs-GaInP approach is described, which allows significant reduction of C-BE and improved high-fre quency performance. A theoretical study of the composite and conventional e mitter HBTs is performed to prove the superiority of composite emitter HBTs using Monte Carlo simulation of their transport properties. The self-align ed HBTs fabricated in this study are grown by C-BE with TBA/TBP precursors. The current gain cutoff frequency (f(T)) was 62 GHz for the composite emit ter design HBT, and 45 GHz for conventional emitter design HBT The C-BE ach ieved with the composite emitter designs was by at least 3 times lower than that of conventional designs and does not show significant variation with collector current. This leads to enhanced f(T) characteristics by 15% for c omposite emitter HBT designs and confirms the theoretical expectations.