Intersubband transitions in non-centrosymmetric quantum wells: 14×14 k·p method

There are experimental observations indicating a need for the revision of intersubband selection rules in D_2d non-centrosymmetric quantum wells (QWs). These observations include (i) the (x,y)-polarized (TE) activities in narrow QWs, (ii) the (x,y)-(TE) and z-(TM) polarized splittings in strained QWs, and (iii) surface-emission of second harmonics generated by using x- and z-polarized intersubband transitions. In this paper we find it crucial to include the band-mixing effects of Γ^c₁₅-Γ^v₁₅ and Γ^c₁₅-Γ^c₁₅ coupling in calculating intersubband transition matrix elements. These two terms are essential to resolve the issues of intersubband TE(x,y)-polarization activities and strain-induced splittings. We find excellent agreement between experimental observations and theoretical investigation