Optical transmittance of thin GaAs wafers upon laser pumping in the region of exciton resonances and the continuum of states: Exciton-exciton interaction

The transmittance spectra of thin “pure” GaAs bulk wafers upon optical pumping corresponding to the band of the ground state of the exciton series are recorded at a temperature of $T$ = 1.7 K. The wafers were grown by molecular-beam epitaxy and vapor-phase epitaxy. An increase in the line amplitude and width upon pumping is observed, with no noticeable changes in the spectral position of the line peak. The increase is similar to that observed upon pumping in the continuum of states, but occurs at a somewhat lower rate. Estimation of the concentration of excitons created by pumping provides a means for determining the exciton-exciton interaction constant and comparing the result with known data. The integrated absorption method makes it possible to refine the exciton polariton-free charge carrier and exciton polariton-impurity interaction constants. The differential photoabsorption of the samples at the pumping modulation frequency is measured. The resultant modulated absorption spectra demonstrate the connection between induced absorption and the formation of differential spectra.