ELECTRON VELOCITY OVERSHOOT EFFECT IN COLLECTOR DEPLETION LAYERS OF INP/INGAAS HETEROJUNCTION BIPOLAR-TRANSISTORS

InP/InGaAs heterojunction bipolar transistors with a 550-angstrom-thick base and 3000-angstrom-thick collector layers are fabricated to study the electron velocity overshoot effect in collector depletion layers. The intrinsic delay time evaluated at room temperature measurement remains almost constant at 0.7-0.8 ps in the investigated base/collector bias range of 0 to 1.1 V at a collector current density of 1 x 10(5) A/cm2. According to Monte Carlo simulation results, such bias-independent behavior is associated with the sufficiently large overshoot effect caused at high collector biases, where the overshoot velocity is enhanced by the high electric field.