Current gain reduction by 0.45 eV oxygen related level in graded band-gap AlGaAs base-emitter of heterojunction bipolar transistors

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Abstract
There are good indications that the deep level around 0.45 eV induced by oxygen acts as an effective electrical recombination center in heterojunction bipolar transistors with a graded band‐gap AlGaAs emitter‐base junction. The transistor, with a concentration of the 0.45 eV level on the order of about 5×1015 cm−3 in the junction region, shows a very small current gain of 3–4, down from more than 30 at a collector current density of 1×103 A/cm3. This reduction is greater than the previously reported one by the level approximately 0.6 eV in heterojunction bipolar transistors. The level about 0.45 eV is detected from the junction region that has an oxygen atom concentration of more than 1018 cm−3. This level may also act as an optically nonradiative recombination center.