Current gain collapse in HBTs analysed by transient interferometric mapping method

Thermal distribution during a current gain collapse event is investigated in multi-finger InGaP/GaAs HBTs using the transient interferometric mapping method. The onset of the collapse is observed at time of about 1ms in devices with a low emitter ballasting resistance R
_E
, while for HBTs with a high R
_E
, the current is distributed equally over the fingers. 3D thermal simulation supports the results and allows an estimation of temperature at which the collapse occurs.