Valence band intersubband electro luminescence from Si/SiGe quantum cascade structures

The principle of intersubband emission is applied to the Si/SiGe material s ystem, using hole intersubband transitions in structures grown pseudo-morph ically on Si substrate by molecular beam epitaxy. Cascade structures consis ting of three times four repetitions of a five quantum well sequence are in vestigated. The design constraints are found to be imposed mainly by the to tal amount of strain, giving limitations to the number of wells per cascade and the total number of cascade periods. Despite the close approach to the critical thickness for misfit dislocations. requiring low temperature grow th, these structures reveal intersubband electro-luminescence with a linewi dth as narrow as 22 meV. Peak energies between 125 and 154 meV are obtained by tuning the well width and Ge content of the single active quantum well. By comparison with the emission from a III-V cascade structure, the non-ra diative lifetime of the upper emission state is determined. It is found to depend strongly on the structure's design, but can reach values comparable to those in similar III-V cascade structures. A discussion of the importanc e of carrier escape to the continuum and the injection efficiency, as well as the relaxation via the light hole state is given. (C) 2001 Elsevier Scie nce B.V. All rights reserved.