ELECTROLUMINESCENCE AND PHOTOLUMINESCENCE STUDIES FROM ULTRATHIN SIMGEN SUPERLATTICES

We have observed strong photoluminescence signals in the near infrared (hv approximately 0.8 eV) from short-period Si(m)Ge(n) strained layer superlattices (SLS) by growing the SLS on a step graded buffer by molecular beam epitaxy [H. Presting and H. Kibbel, Thin Solid Films 222, 215 (1992)]. These luminescence signals are about one order of magnitude stronger than the signals observed so far which can be attributed to the excellent material quality of the SLS which has been achieved by growing at higher temperatures (T(g)=500-degrees-C) and using the technique of Sb surfactant. In addition the SLSs were grown on the step graded buffer which results in a two to three orders of magnitude lower threading dislocation density at the interface compared to the ''simple'' buffers [H. Presting and H. Kibbel, Thin Solid Films 222, 215 (1992); F. K. Le Goues, B. S. Meyerson, and J. F. Morar, Phys. Rev. Lett. 22, 2903 (1991); E. A. Fitzgerald, J.-H. Xie, M. L. Green, D. Brasen, D. R. Kortan, J. Michel, Y.-J. Mii, and B. Weir, Appl. Phys. Lett. 59, 811 (1991) 1. Electroluminescence signals observed from p-i-n-doped diodes with an ''SF''-type buffer show broad signals at a different wavelength the origin of which is still unclear.