Nonlinear optical properties of biexciton states in GaN quantum disks

The ground state energy of an exciton and biexciton states, in a GaN/Al_xGa_1-xN quantum disk are investigated by the variation method, within envelope function and effective mass approximations. Exciton and biexciton binding energy, and the dipole moments related to the transition between ground, exciton and biexciton states, are calculated as a function of quantum disk geometry. The optical nonlinearity via the exciton and biexciton states is studied on the basis of a three level model through the density matrix formalism. The behavior of different terms of third order susceptibility χ⁽³⁾, are studied around resonance frequencies and for different geometries of disk. The effect of values of the decay rates on χ⁽³⁾ are studied. It is found that these values have remarkable effect on the second term of, χ⁽³⁾.