Light-emitting p⁺nn⁺-heterodiode with additional heterojunction in the n-base

It is shown that a p⁺ nn⁺-heterodiode with an additional nn-heterojunction in the n-base can be a very effective light-emitting phototransistor or transistor. A depletion layer of the new intermediate heterojunction splits the n-base into two new bases: wider bandgap phototransistor (transistor) base 1 and narrower bandgap light-emitter base 2. A coefficient of light-to-light conversion (of an input light absorbed in base 1 into an output light emitted in base 2) can be very high due to very high phototransistor gain. Effects of avalanche multiplication in the depletion layer of the intermediate heterojunction, edge multiplication in an accumulation layer of the same junction and thermionic electron emission across a conduction band discontinuity barrier are taken into account. Various material systems appropriate for implementation of the considered device are discussed.