HIGH-PERFORMANCE HETEROJUNCTION BIPOLAR-TRANSISTORS GROWN BY MOLECULAR-BEAM EPITAXY USING NOVEL GROWTH METHOD

A new molecular-beam epitaxial (MBE) growth method is proposed to study the Be diffusion problem in the base of Npn AlGaAs/GaAs heterojunction bipolar transistors (HBTs). The base layer was grown at As-stabilized conditions under minimum V/III beam equivalent pressure of 8 to enhance Be migration and reduce the concentration of nonradiative recombination centers. For a base doping of 4 X 10(19) CM-3 (Be) and emitter dimensions of 2.0 mum X 10 mum, the device demonstrates excellent direct-current as well as microwave performance as a power transistor. The unit current gain cut-off frequency f(T) is 54 GHz and the maximum frequency of oscillation f(max) is above 85 GHz. For power transistors with large emitter periphery (120 mum2), 66% power-added-efficiency and 11 dB power gain have been achieved at 4.5 GHz. After the device was continuously stressed at current densities of 2, 4, and 8 X 10(4) A/CM2, its current gain, h(fe) (measured at stressed current density), turn-on voltage V(be) and junction ideality factor n remain almost identical to the original values. This suggests that heavily Be-doped base AlGaAs/GaAs HBT grown by MBE at low V/III flux ratio may be reliable for small signal-type application in microwave and millimeterwave frequencies.