GaAs/AlGaAs quantum wells with indirect-gap AlGaAs barriers for solar cell applications

We have fabricated GaAs/AlGaAs quantum well (QW) solar cells in which 3 nm-thick QWs and indirect-gap Al0.78Ga0.22As barriers are embedded, and we studied extraction processes of photogenerated carriers in this QW system. The photocurrent under 700 nm light illumination at voltages close to the open-circuit voltage shows only a small reduction, indicating that the carrier recombination inside QWs is largely suppressed. We attribute this result to an efficient extraction of electrons from the QWs through the X-valley of AlGaAs. The insertion of QWs is shown to be effective in extending the absorption wavelengths and in enhancing the photocurrent. The use of indirect-gap materials as barriers is found to enhance carrier extraction processes, and result in an improved performance of QW solar cells.