Abstract

Lattice-mismatch in (111) grown strained layer superlattices (SLS) can give rise to piezoelectric fields on the order of 10⁴-10⁵ V/cm.¹,² These fields lead to interesting nonlinear optical effects, which can depend on the density of free carriers. At low carrier density, there is an effect of the piezoelectric fields on the nonlinear susceptibilities due to parity mixing of the levels: [χ⁽²⁾], and due to piezoelectric field-driven changes in the carrier dispersion relations: [χ⁽³⁾]. In an SLS, grown on a buffer layer intermediate in concentration between the two active epilayers, we use a transfer matrix technique³ to obtain dispersion relations for the superlattice and an exact superlattice wavefunction. This is done within a single band model with momentum mixing of the bands due to zonefolding considered. Using these results we calculate χ⁽²⁾ and χ⁽³⁾ for a CdTe/ZnTe SLS. We find χ⁽²⁾ ~ 10 × bulk GaAs. A large χ⁽³⁾ results because of electric field modulated band nonparaboliticity in the SLS. We find χ⁽³⁾ ~ 60 × bulk GaAs. The level broadening in the minibands demonstrates a strain-induced Franz-Keldysh effect in this system, whose explicit form varies with electric field. Finally, we consider the effect of screening on χ⁽³⁾ as a function of carrier density.

© 1990 Optical Society of America