Bandgap narrowing in strained SiGe on the basis of electrical measurements on Si/SiGe/Si hetero bipolar transistors

We have investigated the bandgap narrowing ΔEgSiGe of strained Si1−xGex layers for 0.15<x<0.29. After MBE layer growth SiGe hetero bipolar transistors (HBTs) are processed by a minimal thermal budget technology to inhibit relaxation and to ensure sharp doping and Ge profiles. ΔEgSiGe is determined by electrical characterisation of the HBTs (gummel plot, temperature dependent measurements). The layer properties are measured by SIMS and TEM. The results show good agreement between room temperature and temperature dependent measurements improving earlier results (J.C. Sturm). This could be achieved by considering the correct temperature dependence of the minority carrier mobility. The obtained ΔEgSiGe is close to the room temperature results of Sturm (0.68x) although a parabolic fit models our data best.