CARRIER-INDUCED OPTICAL NONLINEAR EFFECTS IN SEMICONDUCTOR QUANTUM-WELL WIRE STRUCTURE

Carrier-induced optical nonlinearities in a GaAs quantum well wire structure are calculated within the framework of the effective mass approximation to clarify the nonlinear features of the one-dimensional (1D) system. In the calculation, the excitonic nonlinearity due to phase-space-filling, band-gap renormalization, and Coulomb screening effects is estimated on the basis of an effective 1D Coulomb potential. The 1D potential is derived, taking wire cross section into account. The change in the optical absorption for the band-to-band transition is evaluated, considering the band-filling effect and the changes in the Sommerfeld factor caused by the screening effects. The numerical results show that a blue shift of the excitonic absorption peak occurs at the absorption edge because the blue shift caused by the screening effect exceeds the red shift due to the band-gap shrinkage. In the spectral region above the band edge, where the band-to-band transition determines the optical properties, a decrease in optical absorption caused by band filling is compensated by increasing absorption, which stems from recovery of the Sommerfeld factor because of the Coulomb screening. The effect of the Coulomb interaction in a quantum wire laser is also discussed in relation to the gain spectrum in the high excitation regime. These results show that exact inclusion of the Coulomb interaction is crucial in estimating both linear and nonlinear optical properties in the 1D system.