An AlGaAs double-heterojunction bipolar transistor grown by molecular-beam epitaxy

To study AlGaAs p-n heterojunctions and optical and transport properties of electrically injected minority carriers (electrons) in p-Al0.25Ga0.75As, we have tested the performance of Al0.6Ga0.4As/Al0.25Ga0.75 As/Al0.6Ga0.4As NpN double-heterojunction bipolar transistors (DHBTs). The transistors exhibited a common emitter current gain (β) as high as 400 at a current density of 2 kA cm−2. From the Gummel plots, the ideality factors (n) of emitter-base and base-collector junctions were as low as 1.37 and 1.01, respectively, indicating high quality of both the junctions. Assuming a unity current injection efficiency, we obtain an electron diffusion length of 1.2 μm for an acceptor density of 6.0×1018 cm−3 in p-Al0.25Ga0.75As. Due to the wide band-gap materials, the device has the potential for useful operation at very high temperatures. The device also works as a bright red light emitter when the emitter-base junction is forward biased and the collector is either floating or forward biased, indicating dominance of radiative recombination in the base. Furthermore, the device also works as a phototransistor for detection of short wavelengths (<710 nm) with no sensitivity to longer wavelengths.