Abstract

Short period Si_nGe_m strained layer superlattices have received attention primarily for two reasons. First, there is the possibility of producing a direct-gap group IV material with high luminescence efficiency through zone-folding effects. Second, there is the attraction of making noncentrosymmetric materials (if the periods are odd) that have χ² comparable to GaAs¹ and therefore possess an electro-optic effect and yield strong second harmonic generation. Such materials would be integrable with existing silicon technology. To date, the high luminescence efficiency has not been demonstrated for reasons related to low oscillator strength. Here we show that a large X2 is also not likely for reasons related to subtleties of the structures as they can be grown with present MBE technology.

© 1994 Optical Society of America