Si/Ge0.3Si0.7/Si heterojunction bipolar transistor made with Si molecular beam epitaxy

Abstract

GexSi1−x heterobase n-p-n heterojunction bipolar transistor structure has been grown completely by Si molecular beam epitaxy for the first time. A collector-top type design was adopted. The 3000 Å p-type Ge0.3Si0.7 heterobase layer with 5×1019 cm−3 doping level was grown on an emitter layer which was an arsenic highly doped substrate (7×1019 cm−3), followed by a 5000 Å n-type Si collector layer with 7×1017 cm−3 doping level. Low-temperature device processes under 650 °C were used to avoid thermal diffusion of impurities. Common-emitter current gain hFE with a 100-μm-diam emitter was 15 at 2×104 A/cm2 collector current density. Compared with a usual Si-base bipolar transistor of the same size and doping level, an improvement in current gain was observed. Furthermore, GexSi1−x/Si (x=0.1–0.4) p-n junction interfaces were investigated by current-voltage and capacitance-voltage measurements and transmission electron microscopy observation.