Effects of AlGaAs energy barriers on InAs/GaAs quantum dot solar cells

We have studied the effects of AlGaAs energy barriers surrounding self-assembled InAs quantum dots in a GaAs matrix on the properties of solar cells made with multiple quantum dot layers in the active region of a photodiode. We have compared the fenced dot samples with conventional InAs/GaAs quantum dot solar cells and with GaAs reference cells. We have found that, contrary to theoretical predictions, the AlGaAs fence layers do not enhance the transport properties of photogenerated carriers but instead suppress the extraction of the carriers excited in the dots by light with wavelengths longer than the cutoff wavelength of the GaAs matrix material. Both the standard quantum dots and the fenced dots were found to give solar cell performance comparable to the GaAs reference cells for certain active region thicknesses but neither showed enhancement due to the longer wavelength absorption or improved carrier transport.