Application of the quantum cascade laser principle to the Si/SiGe material system

Summary form only given. The combination of Si technology for both electronics and active optical components has always attracted a great deal of interest, but so far, the indirect bandgap of this group IV material prevented the fabrication of an efficient light emitter. This obstacle can be circumvented by adopting the concept of the quantum cascade laser (QCL) to the Si/SiGe material system. QCLs rely on intersubband transitions and tunneling, which are not dependent on the type of the bandgap. While the non-polar character of SiGe alloys is an advantage, the large lattice mismatch between Si and Ge, small band offsets in the complex valence band, and large effective masses for holes are severe drawbacks for QCL fabrication. Two intersubband luminescence structures, whose main difference is the width of the optically active quantum well, were grown by low temperature MBE. The structure is a repetition of twelve periods consisting of one injector region and one optically active quantum well each. Two heavy hole (HH) states and one light hole (LH) state are confined in the optically active quantum well. The aim of the injector is to fill the upper level HH2 with carriers, which then make a radiative transition down to the ground state HH1. Holes can escape from this level via tunneling through a miniband provided by the injector region of the subsequent period.