Suppression of phototransistor gain in an optical modulator

Abstract

An optical modulator (50) includes an emitter layer (32) with N-type doping having a first bandgap energy; a base layer (34) with P-type doping having a second bandgap energy; and a sub-emitter layer (54) disposed between the emitter layer (32) and the base layer (34), wherein the sub-emitter layer (54) has a third bandgap energy that is less than both the first bandgap energy and the second bandgap energy. The optical modulator (50) can further include a collector layer (16) having N-type doping; and an undoped layer (12) between the collector layer (16) and the base layer (34). The sub-emitter layer (54) provides a barrier to electrons flowing from the emitter layer (32), while allowing photo-generated holes to recombine in the sub-emitter layer (54) thereby mitigating current amplification.

Dependencies are inferred from the claim text.