Supergain transistors on high-purity float-zone silicon substrate

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Since float-zone (FZ) silicon has lower contamination and longer minority carrier lifetime than those in Czochralski silicon and other semiconductor materials, it has potential advantages to fabricate a bipolar junction transistor on the FZ substrate to achieve high gain at very low current levels. In this report, the authors present preliminary experimental results on supergain bipolar junction transistors fabricated on unusual FZ refined high-resistivity silicon substrate and by ion implantation technology. A phosphorus-doped polycrystalline silicon backside gettering layer has been employed to preserve the long carrier lifetime of the high-purity FZ silicon. Bipolar junction transistors have demonstrated high current gain, more than 3300 for ultralow base current levels of 10 pA in this study. Possible applications of high-purity FZ silicon on some advanced semiconductor devices and circuits are discussed in this letter.