Management of highly-strained heterointerface in InGaAs/GaAsP strain-balanced superlattice for photovoltaic application

We report an implementation of a strain-balanced superlattice structure in a photovoltaic device. A thin-period structure is an appropriate design for a strain-balanced epitaxy allowing minimum stress accumulation in the highly strained quantum well (QW). However, a large number of interfaces cause a serious issue as critical as strain balancing. Such a structure suffers from degraded crystal quality with the increase of number of interfaces; and the atomic contents within the well or barrier also become difficult to control. With help from in situ reflectivity measurement and x-ray diffraction, it was deduced that such an interface issue could result from unpredictable interfacial strain relaxation and irregular interface morphology between strained well and barrier. According to this mechanism, we developed a smart interface management, insertion of a monolayer-thin strain-neutral GaAs, to avoid diffused interfaces and morphology degradation. The modified superlattice solar cell exhibits good performance.