EXPERIMENTAL EVALUATION OF SEPARATE CONTRIBUTIONS TO IDEALITY FACTOR FOR THE BASE SURFACE RECOMBINATION CURRENT IN HETEROJUNCTION BIPOLAR-TRANSISTORS

In this paper it is shown experimentally, for the first time, that the ideality factor n for the extrinsic base surface recombination curren t in AlGaAs/GaAs heterojunction bipolar transistors (HBTs) is unity an d is bias independent. The devices with various emitter radii have bee n fabricated and the n = 1 and n = 2 current components of the emitter -base junction current were calculated. It was observed experimentally that the n = 1 current component was proportional to the total area o f the emitter-base junction plus the exposed extrinsic base surface, b oth at lower biases such as emitter-base voltage V-BE 0.60 V (when the n = 2 current component dominates), and at higher biases such as V-BE = 1.0 V (when the n = 1 current component dominates). The ideality fa ctor value for the diffusion current is 1. Therefore, these results su ggest that the ideality factor of the extrinsic base surface recombina tion current in HBTs is unity and is independent of the emitter-base b ias.