(Ga,Al)As/GaAs bipolar transistors for digital integrated circuits

(Ga,A1)As/GaAs npn bipolar transistors have been made using MBE growth. The epitaxial layer structure has been designed for high speed integrated circuit operation, and base regions as thin as 1000Å with p = 10¹⁹cm^-3have been utilized. Fabrication processes based on both selective etching and Be implantation (to achieve a planar structure) have been demonstrated. Effects which influence current gain of the transistors are discussed. It is projected that current-mode-logic ICs based on scaled transistors of this type will achieve propagation delay times of 20-25 ps at an associated speed-power product of 70 fJ (unity fan-in and fan-out).