HETEROJUNCTION BIPOLAR-TRANSISTORS IN ALGAINP/GAAS GROWN BY METALORGANIC VAPOR-PHASE EPITAXY

A series of low-pressure metalorganic vapor phase epitaxy grown Al xGa0.52-xIn0.48P/GaAs single heterojunction bipolar transistors with x=0, 0.18, 0.30, 0.40, and 0.52 have been studied. These devices consistently exhibit near-ideal characteristics with base and collector current ideality factors close to unity except in the ungraded AlInP case. A low conduction band spike height which is believed to be due to unintentional grading at the emitter-base junction of the partially graded devices (intentionally graded down close to the Ga0.52In 0.48P lattice-matched composition) provides effective hole current suppression over the whole range of compositions. Base bulk recombination current was determined to be the current-gain limiting mechanism for x≤0.3 in this heterojunction bipolar transistors (HBT) system. The common-emitter dc current gain showed a maximum value of 380 at JC=4×10 3 A/cm2 for x=0.18 which translates to a minority electron diffusion length of 1.1 μm. These are the highest values reported for a base sheet resistance of 440 Ω/D'Alembertian sign. © 1994 American Institute of Physics.