Effect of Piezoelectric Fields on the Bandstructure and Nonlinear Susceptibilities of Certain II-VI Strained Layer Superlattices

In a piezoelectric material, strain gives rise to internally generated polarization fields. These electric fields modify the band structure and optical properties of the material. We have calculated the lattice mismatch strain for pseudomorphically grown Hg sub (1-x) Cd sub (x) Te/Hg sub (1-y) Zn sub y Te strained layer superlattices (SLS) (which have large electro-optic coefficients) for x = y = .9 and x = .67, y = .9. The strain (~0.5) gives rise to piezoelectric fields as large as 1.5 x 10 sup 4 V/cm in alternating layers. We calculated the modified band structure in the growth direction due to these fields. We then calculated the nonlinear susceptibilities chi sup (2) and chi sup (3) which can show enhancements at certain frequencies, in the presence of the piezoelectric fields. The effect of valence band offset and ratio of exciton Bohr radius to epilayer width is important.