Wavelength dependence of combined local and carrier transport optical nonlinearities in a hetero n-i-p-i structure

The combination of carrier transport-type optical nonlinearity and absorption saturation is examined for a hetero n-i-p-i sample at wavelengths between 966 and 985 nm and for intensities up to 1000 W cm2. Transmission changes are found to depend on the interplay between the shift, narrowing, and increasing peak height of an excitonic absorption resonance. Transmission changes previously attributed to absorption saturation are found to be due to carrier transport nonlinearity. Absorption saturation contributed to transmission change for intensities greater than 100 W cm2, a larger value than previously reported; however saturation intensity still appears to have been reduced by charge separation and a correspondingly slower electron-hole relaxation rate.