Sketch of the photon absorption and carrier transportation processes of InAs quantum dots embedded in GaAs with a p–n junction. (a) Schematic diagram of the established photon absorption and carrier transportation processes. When a photon with energy hv > E_g incidents to the sample, the high excited state free electron–hole pair generate, and then relax to the ground state, finally the electron–hole pair recombine and emit a photon. (b) Schematic diagram of the new photon absorption and carrier transportation processes. InAs quantum dots embedded in GaAs with a p–n junction under the short-circuit condition. When a photon with energy hv > E_g incidents to the sample, the high excited state free electron–hole pair generate, and then escape directly from InAs quantum dots to external circuit under the driving force of the build-in electric field.