LIMITATIONS TO THE REALIZATION OF NONCENTROSYMMETRIC SIMGEN SUPERLATTICES

Citation
Dj. Bottomley et al., LIMITATIONS TO THE REALIZATION OF NONCENTROSYMMETRIC SIMGEN SUPERLATTICES, Physical review. B, Condensed matter, 50(12), 1994, pp. 8564-8568
Citations number
16
Categorie Soggetti
Physics, Condensed Matter
ISSN journal
01631829
Volume
50
Issue
12
Year of publication
1994
Pages
8564 - 8568
Database
ISI
SICI code
0163-1829(1994)50:12<8564:LTTRON>2.0.ZU;2-U
Abstract
We extend the work of Bottomley et al. [Appl. Phys. Lett. 63, 2324 (19 93)] on second-harmonic generation from short-period (SimGen)(p) strai ned-layer superlattices (SLS) with n and m both odd integers. Such str uctures are theoretically predicted to be noncentrosymmetric and there fore should possess a large bulk, nonlinear susceptibility chi((2)). H owever, the prior work showed that the inevitable presence of single a tomic-height steps on the Si(001) substrate leads to the formation of antiphased domains within the SLS and hence a macroscopically centrosy mmetric material. Here we report second-harmonic generation induced by a 775-nm beam on several samples of nominally (Si7Ge3)(20) SLS's grow n on several substrates vicinal to Si(001), including those with biato mic-height steps; the latter substrates should allow in-phase domains to be grown. A nonzero, but weak bulk chi((2)) is obtained. We propose that the weak nonlinear response is influenced by nonideal superlatti ce periodicity which results in the formation of antiphase domains alo ng the growth direction. Suggestions are offered for how noncentrosymm etric SLS's may eventually be realized.