Heterojunction bipolar transistor fabrication using Si1−xGex selective epitaxial growth by gas source silicon molecular beam epitaxy

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Abstract
B doping in Si1−xGex was successfully achieved using HBO2 cell in gas source Si molecular beam epitaxy (Si‐MBE). Combining this B doping method and selective epitaxial growth of Si1−xGex by gas source Si‐MBE, B‐doped Si1−xGex selective epitaxial growth was found to be possible. This B‐doped Si1−xGex selective epitaxial growth was applied to Si1−xGex/Si heterojunction diode and Si1−xGex base heterojunction bipolar transistor (HBT) fabrications. The Si1−xGex base HBT (x=0.16, 0.22, 0.31) showed higher hFE in as‐grown condition than that for a homojunction transistor. The band‐gap difference between the Si1−xGex base and the Si emitter was estimated by the temperature dependence of the collector current ratio between the HBT and the homojunction transistor.