MONTE-CARLO ANALYSIS OF NONEQUILIBRIUM ELECTRON-TRANSPORT IN INALGAAS/INGAAS HBTS

We report a Monte Carlo analysis of nonequilibrium electron transport in InAlGaAs/InGaAs HBT's. The discussion focuses on hot electron transport in a heavily doped p-type base from the viewpoint of high-speed transistor performance. Simulation shows that a hybrid base structure which incorporates an abrupt emitter/base junction and a graded base layer has a shorter base transit time than conventional uniform base structures with an abrupt emitter or fully graded base structures. The short base transit time is due to the high initial electron velocity provided by the abrupt emitter/base junction and the acceleration of energy-relaxed electrons (which cause a lowering of average electron velocity in the base region) by a built-in electric field in the graded base layer. We also mention the influence of hot electron injection into the collector.