Submicron-square emitter AlGaAs/GaAs HBTs with AlGaAs hetero-guardring

Successful operation of submicron-square emitter AlGaAs/GaAs HBTs is demonstrated for the first time by using a fully mesa-structure-type emitter-base junction-area definition method with an AlGaAs hetero-guardring. The hetero-guardring reduces surface recombination current at the emitter-mesa edge to 1.4 μA/μm. This is 1/10 of that for devices without the guardring. Here, dc gains of 20, 26, and 40 are achieved for 0.5 μm×0.5 μm, 0.7 μm×0.7 μm, and 0.9 μm×0.9 μm emitter HBTs, respectively. An f_T of 40 GHz, and an f_max of 30 GHz are obtained for 0.9 μm×0.9 μm at a J/sub C/ of 1.0×10⁵ A/cm².