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 4×1019 cm−3 (Be) and emitter dimensions of 2.0 μm×10 μm, the device demonstrates excellent direct‐current as well as microwave performance as a power transistor. The unit current gain cut‐off frequency fT is 54 GHz and the maximum frequency of oscillation fmax is above 85 GHz. For power transistors with large emitter periphery (120 μm2), 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 8×104 A/cm2, its current gain, hfe (measured at stressed current density), turn‐on voltage Vbe and junction ideality factor n remain almo...