Coexistence of deep levels with optically active InAs quantum dots

We present direct experimental evidence of the coexistence of deep levels with intrinsic quantum confinement states in large, self-assembled InAs quantum dots embedded in a GaAs matrix. The InAs quantum dots show very good optical properties, as evidenced by the strong photoluminescence at room temperature at similar to 1.3 mu m. Deep levels 160 and 484 meV below the GaAs conduction band edge have been identified at large reverse biases and high temperatures using deep level transient spectroscopy (DLTS) measurements. The reverse-bias dependence of the DLTS signal together with experimental results from the reference samples, containing thin InAs layers but no quantum dots, confirms that the deep levels coexist in the same layer as the InAs dots, and are most likely caused by the strain field during the lattice mismatched growth process. The densities of the deep levels in the structure are comparable to the density of the optically active quantum dots.