Band structure and optical properties of sinusoidal superlattices: ZnSe1-xTex

This paper examines the band structure and optical selection rules in super lattices with a sinusoidal potential profile. The analysis is motivated by the recent successful fabrication of high duality ZnSe1-xTex superlattices in which the composition x varies sinusoidally along the growth direction. Although the band alignment in the ZnSe1-xTex sinusoidal superlattices is s taggered (type II), they exhibit unexpectedly strong photoluminescence, thu s suggesting interesting optical behavior. The band structure of such sinus oidal superlattices is formulated in terms of the nearly-free-electron (NFE ) approximation, in which the superlattice potential is treated as a pertur bation. The resulting band structure is unique, characterized by a single m inigap separating two wide, free-electron-like subbands for both electrons and holes. Interband selection rules are derived for optical transitions in volving conduction and valence-band states at the superlattice Brillouin-zo ne center, and at the zone edge. A number of transitions are predicted due to wave-function mixing of different subband states. It should be noted tha t the zone-center and zone-edge transitions are especially easy to distingu ish in these superlattices because of the large width of the respective sub bands. The results of the NFE approximation are shown to hold surprisingly well over a wide range of parameters, particularly when the period of the s uperlattice is short.