Experimental values for the hole diffusion coefficient and collector transit velocity in P-n-p AlGaAs/GaAs HBTs

The diffusion coefficient (D/sub h/) and a value for the collector velocity (v/sub h/) of holes in AlGaAs/GaAs P-n-p HBTs (heterojunction bipolar transistors) were obtained from high-frequency measurements on structures with different base and collector widths. Quantities for D/sub h/ and v/sub h/ of 5.6 cm/sup 2//s and 5.5*10/sup 6/ cm/s, respectively, were obtained by plotting the total emitter-collector delay versus inverse emitter current and extrapolating the data to infinite emitter current to obtain the base and collector transit delays. An f/sub t/ and f/sub max/ as high as 15 and 29 GHz, respectively, were obtained for non-self-aligned (1- mu m emitter mesa/base contact separation) devices with a 2.6- mu m*10- mu m emitter.>