CHARGE-COLLECTION MECHANISMS OF ALGAAS GAAS HBTS/

AlGaAs/GaAs heterojunction bipolar transistors are investigated via ti me-resolved and time-integrated laser induced charge-collection measur ements and by two-dimensional computer simulation. Both experiment and simulation results suggest that charge collection occurs by a simple model in which carriers created by the ionizing event are collected at the device terminals, with no evidence for charge enhancement process es. The charge-collection efficiency in all cases is less than unity, with the collected charge exhibiting a linear dependence on the deposi ted charge for all laser wavelengths used (below the saturation limit) . The simulation results reveal that the fast and slow contributions t o the charge collection transient arise from electron and hole collect ion, respectively, with the lower mobility of the holes giving rise to their slower collection dynamics.