Photocurrent Generation by Two-Step Photon Absorption With Quantum-Well Superlattice Cell

We have observed photocurrent due to two-step photon absorption using an InGaAs/GaAsP strain-balanced quantum-well (QW) superlattice cell, with barrier thickness of 3 nm. Upon infrared irradiation with a filtered air mass 1.5 light source (λ > 1.4 μm), quantum efficiency was increased by 0.8% at the wavelength range corresponding to the absorption of the quantum wells. No efficiency enhancement was observed either for a conventional QW solar cell with thick (11 nm) barriers or for a GaAs pin cell, suggesting that efficient separation of photogenerated electrons and holes in the superlattice is essential for this achievement of two-step photon absorption. The quantum efficiency of such two-step photocurrent generation can be enhanced by specific tailoring of a superlattice layer structure, by which the QW superlattice will be a possible active region for an intermediate-band solar cell.