Coulomb screening induced by electrons trapped on interface of InAs/InGaAs quantum dots

InAs quantum dots are actively researched nanostructures for photonic and electronic devices. Metamorphic InAs/InGaAs quantum dot structures are III-V nanostructures with wider design possibilities as compared to the conventional pseudomorphic InAs/GaAs quantum dot structures. However, for photonic applications of these nanostructures, the effect of defect levels still needs in-depth investigation. We have focused on th e nfluence of electron traps of defects on photocurrent in plane of InAs/InxGa1-xAs quantum dot arrays with x = 0.15 or 0.31, grown by molecular beam epitaxy on GaAs substrates. The structures are studied by photocurrent and deep level thermally stimulated current spectroscopy together with HRTEM and theoretical modeling. The arrays are found to be photosensitive in the telecommunication ranges at 1.3 and 1.55 ?m, respectively. In the structures, a rich spectrum of electron trap levels of point defects EL6, EL7, EL8, EL9/M2, EL10/M1, M0 and three extended defects ED1/EL3, ED2/EL4, ED3/EL5 has been identified. Among them, new defect levels undiscovered earlier in InAs/InGaAs nanostructures has been detected, in particular, EL8 and M0. The found electron traps are shown to slow the time-dependent photocurrent at low temperatures. Besides a long-term kinetics due to trap charging, a prolonged photocurrent decrement versus time is measured under constant illumination. The decrement is interpreted to be related to a Coulomb screening/narrowing of the wetting layer conductivity channel of the array by the electrons captured in the quantum-dot-buffer interface, which is commonly assumed to have trap levels originated by the interdiffusion of the constituent atoms and from plastic strain relaxation. The decrement is well fitted by allometric exponents, which means many types of traps are involved in electron capturing. This study provides new findings into the mechanism of photoc urrent in plane of quantum dot layers, showing a crucial importance of growth-related interface defects of nanostructures on photoresponsivity at low temperatures.