NONLINEAR OPTICAL-PROPERTIES OF GAAS/GA1-XALXAS SUPERLATTICES

We calculate the third-order nonlinear optical susceptibility, (3), of the GaAs/Ga0.7Al0.3As superlattice by determining the enhanced band nonparabolicity in the superlattice growth direction. A four-band kp model is used for the band structure of the bulk semiconductors, and the superlattice conduction minibands are obtained using a transfer-matrix method developed earlier. Estimates for (3), averaged over the Fermi distribution of energies, are made at T=0 K and at room temperature. The calculations are performed for a number of representative values for carrier concentrations in the conduction minibands and for various layer thicknesses. In-plane nonparabolicity is incorporated, and no approximations are made for the Fermi distribution of carriers over the lowest and the first excited minibands. For the GaAs/Ga1-xAlxAs superlattice it is found that the in-plane nonparabolicity has a negligible effect on (3) both at T=0 and 300 K. For T=0 K, a superlinear behavior of (3) with carrier concentration is obtained for Fermi energies near the top of the lowest miniband. We find that significant contributions to (3) occur from the first excited miniband in the case of wide wells, and that the magnitude of (3) is enhanced for wider wells and/or barriers. © 1990 The American Physical Society.