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

Abstract

Ge_xSi_1−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 Ge_0.3Si_0.7 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 h_FE 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, Ge_xSi_1−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.