Search

Polycrystalline GeSn thin films on Si substrates with a Sn composition up to 4.5% have been fabricated and characterized. The crystalline structure, surface morphology, and infrared (IR) absorption coefficient of the annealed GeSn thin films were carefully investigated. It was found that the GeSn thin films with a Sn composition of 4.5% annealed at 450 °C possessed a desirable polycrystalline structure according to X-ray diffraction (XRD) analyses and Raman spectroscopy analyses. In addition, the absorption coefficient of the polycrystalline GeSn thin films in the IR region was significantly better than that of the single crystalline bulk Ge.

The effects of proton irradiation on SiGe HBTs implemented with isolation guard rings are investigated in this work. Different from what was shown in any of the previous radiation tolerance studies, a distinctive increase of the emitter current after proton irradiation was observed on a measured inverse-mode Gummel plot from the SiGe HBTs implemented with isolation guard rings. Detailed device measurements and modeling revealed a new SiGe HBT degradation mechanism under proton irradiation. It is found that the increase of the emitter current measured in the inverse-mode Gummel plot comes from the degradation of the substrate–collector (buried layer) junction diode associated with the SiGe HBTs. Furthermore, we identified that the radiation damages in the substrate–collector junction near the deep trench edges are solely responsible for the observed degradation of radiation tolerance. The potential impact of this radiation damage to device operation is discussed.

The performance of a SiGe heterojunction bipolar transistor (HBT) millimetre-wave power amplifier (PA) operating at cryogenic temperature was reported and analysed for the first time. A 24 GHz two-stage medium PA employing common-emitter and common-base SiGe power HBTs in the first and the second stage, respectively, showed a significant power gain increase at 77 K in comparison with that measured at room temperature. Detailed analyses indicate that cryogenic operation of SiGe HBT-based PAs mainly affects (improves) the performance of the SiGe HBTs in the circuits due to transconductance enhancement through magnified, favourable changes of SiGe bandgap due to cooling (ΔEg/kT) and minimized thermal effects, with little influence on the passive components of the circuits.