EXCITON BIEXCITON ENERGIES IN RECTANGULAR GAAS/ALXGA1-XAS QUANTUM-WELL WIRES INCLUDING FINITE AL-GRADED BAND OFFSETS WITH APPLICATION TO 3RD-ORDER OPTICAL SUSCEPTIBILITIES/

Exciton and biexciton binding energies and wave functions are calculat ed with a three-parameter variational model in an effective-mass appro ximation for a rectangular GaAs quantum-well wire surrounded by an Al- x,Ga1-xAs cladding. Moreover, the Al interdiffusion into the wire and the finite band offsets between the wire and the cladding have been in cluded. For the range of dimensions studied, the inclusion of the Al i nterdiffusion had a pronounced effect on the binding energies when com pared to those obtained from the infinite barrier model [Frank L. Mada rasz, Frank Szmulowicz, F. Kenneth Hopkins, and Donald L. Dorsey, Phys . Rev. B 49, 13528 (1994); J. Appl. Phys. 75, 639 (1994); Phys. Rev B 51, 4633 (1995)]. Using the results of the exciton and biexciton calcu lation, we calculate the third-order nonlinear optical susceptibility as a function of pump-probe frequencies in a small range about the exc iton absorption resonance. We have found, depending upon wire dimensio ns, broadening parameter(s) size, and the amount of pump detuning, val ues of the imaginary parts of the susceptibilities to be on the order of -10(-1) esu and a fairly large off-resonance absorption due to biex citon formation.