Improved high frequency performance of AlInAs/GaInAs HBTs through use of low temperature GaInAs

GaInAs grown at lower than normal substrate temperatures was used to reduce the amount of beryllium out-diffusion from the heavily doped bases of AlInAs/GaInAs Npn HBTs. A combined 20-nm-thick spacer structure of p-doped and undoped GaInAs grown at 300 degrees C prevented excessive amounts of beryllium from diffusing into the AlInAs emitter. This allowed base beryllium doping concentrations up to 10/sup 20/ cm/sup -3/ to be achieved, thereby reducing base resistance and increasing f/sub max/ to 70 GHz. A fifteen-stage ring oscillator utilizing these HBTs demonstrated a gate delay of 15.8 ps. The reduced outdiffusion was confirmed by secondary ion mass spectrometry (SIMS) elemental profiles in addition to electrical measurements.<
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