Effect of irradiation by He⁺ and Ga⁺ ions on the 2D-exciton susceptibility of InGaAs/GaAs quantum-well structures

The effect of irradiation by 30‐keV Ga+ and 35‐keV He+ ions (in relatively small doses) on the excitonic reflectivity spectra of single InGaAs/GaAs quantum‐well structures is studied. It is found that the irradiation results in decreasing intensity and broadening of the excitonic resonances in the reflectivity spectra for all the doses. It is shown that these changes are not related to a decrease of the exciton transition oscillator strength and, therefore, to the irradiation‐induced destruction of the excitonic states, but can be rather ascribed to a common cause, namely, to inhomogeneous broadening of the excitonic resonances proportional to the exposure dose. A tentative model of the irradiation‐induced broadening is considered, with the mechanism of the process being a consequence of scattering of the 2D excitons by structural defects associated with Ga(In) and As vacancies arising upon collisions of the high‐energy ions with regular atoms of the crystal structure. The model is used to compare experimental dependence of efficiency of the Ga+‐ion‐induced broadening on distance of the quantum well from the irradiated surface with a similar dependence calculated using the Monte‐Carlo technique. A discrepancy between the results of simulation and experimental data is discussed.