PLANAR, AL0.3GA0.7AS-PASSIVATED-BASE, HETEROJUNCTION BIPOLAR PHOTOTRANSISTORS

New planar GaAs heterojunction bipolar phototransistors have been desi gned and demonstrated. The devices use a GaAs/Al0.3Ga0.7As molecular-b eam-epitaxy materials system with an Al0.3Ga0.7As passivated, 10-nm-th ick base; a depleted, high-low emitter; and a low emitter-base capacit ance. Electrical contact to the emitter is made by a set of parallel, ohmic fingers and to the collector by an ohmic contact formed in a lar ge, approximate to 1.48-mu m deep via. Rise times in response to impul se optical excitation at 810 nm were 747-891 ps except at the two lowe st optical excitation powers measured. Photocurrent gains measured at 810 and 850 nm were 0.67-19, depending on experimental conditions. The se devices are promising for use in heterodyne photodetector arrays fo r coherent optical processing channelizers requiring a 100-MHz bandwid th.