Influence of localization on the carrier diffusion in GaAs/(Al,Ga)As and (In,Ga)(As,N)/GaAs quantum wells:: A comparative study

Using a spatially resolved cathodoluminescence technique, we measure the detection-energy and temperature dependence of the diffusion length of excited carriers in GaAs/(Al,Ga)As and (In,Ga)(As,N)/GaAs single quantum wells (QWs), for which the sources of disorder are expected to be entirely different. While in GaAs QWs the interface roughness is a possible source of disorder, in (In,Ga)(As,N) QWs the compositional inhomogeneities are expected to be the prime cause of band structure fluctuations. Thus, the density of the disorder is expected to be even larger in (In,Ga)(As,N)/GaAs QWs as compared to the one in GaAs/(Al,Ga)As QWs. We found that the detection energy as well as temperature dependence of the diffusion length in the two systems are distinctly different. The experimental results are explained in terms of a thermally activated transport in GaAs/(Al,Ga)As QWs and a tunneling-assisted transport in (In,Ga)(As,N)/GaAs QWs. The detection-energy and temperature dependence of the diffusion length can be a powerful tool to distinguish between these two transport mechanisms. Moreover, we have developed a simple theoretical model in order to obtain a better understanding of the diffusion process in (In,Ga)(As,N)/GaAs QWs.