DC and AC Performances in Selectively Grown SiGe-Base HBTs (Special Issue on High-Frequency/speed Devices in the 21st Century)

概要

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A selectively grown Si_<1-x> Ge_x base heterojunction bipolar transistor (HBT) was fabricated, and effects of Ge and B profiles on the device performance were investigated. Since no obvious leakage current was observed, it is shown that good crystallinity of Si_<1-x> Ge_x was achieved by using a UHV/CVD system with high-pressure H_2 pre-cleaning of the substrate. Very high current gain of 29,000 was obtained in an HBT with a uniform Ge profile by both increasing electron injection from the emitter to the base and reducing band gap energy in the base. Since the Early voltage is affected by the grading of Ge content in the base, the HBT with the graded Ge profile provides very high Early voltage. However, the breakdown voltage is degraded by increasing Ge content because of reducing bandgap energy and changing dopant profile. To increase the cutoff frequency, dopant diffusion must be suppressed, and carrier acceleration by the internal drift field with the graded Ge profile has an additional effect. By doing them, an extremely high cutoff frequency of 130 GHz was obtained in HBT with graded Ge profiles.
社団法人電子情報通信学会の論文
1999-11-25