GaAs/Si Tandem Solar Cells with an Optically Transparent InAlAs/GaAs Strained Layer Superlattices Dislocation Filter Layer

Abstract

Epitaxial growth of III-V materials on Si is a promising approach for large-scale, relatively low-cost, and high-efficiency Si-based multi-junction solar cells. Several micron-thick III-V compositionally graded buffers are typically grown to reduce the high threading dislocation density that arises due to the lattice mismatch between III-V and Si. Here, we show that optically transparent n-In0.1Al0.9As/n-GaAs strained layer superlattice dislocation filter layers can be used to reduce the threading dislocation density in the GaAs buffer on Si while maintaining the GaAs buffer thickness below 2 mu m. Electron channeling contrast imaging measurements on the 2 mu m n-GaAs/Si template revealed a threading dislocation density of 6 x 10(7) cm(-2) owing to the effective n-In0.1Al0.9As/n-GaAs superlattice filter layers. Our GaAs/Si tandem cell showed an open-circuit voltage of 1.28 V, Si bottom cell limited short-circuit current of 7.2 mA/cm(2), and an efficiency of 7.5%. This result paves the way toward monolithically integrated triple-junction solar cells on Si substrates.