Electrical characteristics of double-base Si/Si1−xGex/Si heterojunction bipolar transistors

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Recent advances in low-temperature epitaxial growth of strained, single-crystalline silicon–germanium random alloys (Si1−xGex) have introduced band gap engineering into the design of silicon-based devices. Here we describe a novel device, the double-base heterojunction bipolar transistor, which increases the functionality of a ‘‘normal’’ Si/Si1−xGex/Si heterojunction bipolar transistor by having two base contacts which can independently control the collector current. It can be used in a single-transistor NAND gate at temperatures up to 140 K, as an amplifier with digital ON/OFF control, or to increase the Early voltage (output resistance). In this article, the fabrication procedure of the device is outlined in detail, followed by complete electrical evaluation and modeling.