GaAs quantum well laser and heterojunction bipolar transistor integration using molecular beam epitaxial regrowth

To explore monolithically integrated phototransmitters, a graded-index quantum well laser was integrated with a selectivity regrown heterojunction bipolar transistor (HBT). The laser utilized a p-up configuration, and the HBT used collector down geometry. This scheme allowed the devices to be interconnected through the n+-GaAs substrate. The threshold current (Ith) for the ridge waveguide laser was ∼70 mA. The HBT exhibited a small signal gain of 26 at a collector current of 30 mA. The modulation index defined as the change in light output per unit change in base current is 1.2 mW/mA for our device.