Photoluminescence investigation of Be-doped Npn AlGaAs/GaAs heterojunction bipolar transistor structures

Highly complex Npn AlGaAs/GaAs single heterojunction bipolar transistor (HBT) layers with Be-doped base were investigated by photoluminescence (PL) spectroscopy. Room temperature PL shows only a broad peak of GaAs due to thermalization; 15 K PL shows five peaks. The peak at ∼1.481 eV is from a p-type GaAs base, that at ∼1.517 eV is from a low-doped GaAs layer and that at ∼1.55 eV is from a high-doped GaAs collector. The that at ∼1.849 eV is due to bound exciton recombination in an AlGaAs emitter, and that at ∼1.828 eV is due to the acceptor-related transition from the AlGaAs layer. The integrated intensity ratio of these two peaks can be used to investigate the Be outdiffusion behavior, thus optimizing the growth conditions of base. The DC current gain of the HBT structure with different growth conditions was found to be in good agreement with the PL results.