Bandgap and Strain Engineering in SiGeC Heterojunction Bipolar Transistors

The incorporation of C into Si1-x Ge x alloys contributes to enlarging the critical layer thickness and to improving the thermal budget. It also realizes a narrower bandgap with compensated strain. These effects would introduce good performance at high frequency in the devices. We fabricate heterojunction bipolar transistors (HBTs) with an Si1-x-y Ge x C y base layer using ultrahigh-vacuum chemical vapor deposition (UHV-CVD) technology. The bandgaps of Si1-x-y Ge x C y base layers are measured by the evaluation of the collector current dependence on temperature. The strain of the pseudomorphic Si1-x-y Ge x C y layer is also extracted by an analysis of the X-ray diffraction spectra. Good flexibility of Si1-x-y Ge x C y alloy is shown for the bandgap and strain engineering. The devices using the excellent characteristics of Si1-x-y Ge x C y alloy have numerous applications for wireless telecommunications.