Study on New Emitter Structure Using Ultra-Thin Silicon Carbide Films as Hole Blocking Layr

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It is possible to reduce the base resistance by introducing wider energy bandgap emitter than a base region. This can make operation speed of bipolar transistor faster. We proposed amorphous SiC (a-SiC) and microcrystalline Si (mu c-Si) for the emitter material and fabricated prototype devices using those. For only using mu c-Si the device showed low current gain because of epitaxial growth which forms the Si homojunction. Whereas, we fabricated devices with a a-SiC ultra-thin film before deposition of a mu c-Si film, resulting in 20-30 times larger current gain than that of the mu c-Si device. However emitter resistance of the a-SiC device increased, which degraded high frequency performance.Nextly, we attempted to fabricate devices having SiGe base as a narrow bandgap base. SiGe films were formed by sputtering Si and Ge targets using an Ar ion beam. Epitaxial temperature went down by adding Ge. For example, the epitaxial temperature was as low as 400ﾟC for composition of Si_<.75>Ge_<.25>.Furthermore, we investigated low temperature Si epitaxial growth by ECR (Electron Cycrotron Resonance) plasma CVD method. In the film growth process, not only deposition process but also etching process was found to proceed. The later process was found to be effective for enhancing epitaxial growth. Moreover, selective epitaxial growth was successfully carried out by controlling the deposition conditions.