AlGaAs-GaAs heterojunction phototransistors for fiber-optical communications

The metalorganic chemical vapor deposition technique has been used to grow Al0.5Ga0.5As-GaAs wide gap emitter n-p-n heterojunction phototransistor structures. These devices have base regions 0.25 µm thick. The measured optical gain, G, of floating base devices is 200 at high injection levels, and this corresponds to a minority carrier diffusion length of Ln=2.5 µm. Similar values are obtained for β in the common-emitter configuration with devices which have a base contact. The spectral response of these detectors is nearly constant from 0.86 to 0.65 µm.