High Performance Metamorphic Tunnel Junctions for GaAsP/Si Tandem Solar Cells Grown via MOCVD

A high-performance metamorphic $\mathbf {Al}_{\mathbf {0.2}} \mathbf {Ga}_{\mathbf {0.8}} \mathbf {As}_{\mathbf {0.75}} \mathbf {P}_{\mathbf {0.25}}$/GaAs$_{\mathbf {0.75}}{\mathbf {P}}_{\mathbf {0.25}}$ tunnel junction structure, grown by metal-organic chemical vapor deposition, was designed for use within GaAs$_{\mathbf {0.75}} {\mathbf {P}}_{\mathbf {0.25}}$textbf/Si tandem solar cells. Optimized growth conditions were determined for high C (p-type) and Te (n-type) doping, and a method to mitigate the well-known Te memory effect was develop. The optimized as-grown standalone test device yielded a peak tunneling current of 279.1 Acm $^{\mathbf {-2}}$ and zero-bias resistance-area product of $3.0 \times 10^{\mathbf {-4}} \Omega \mathbf {cm}^{\mathbf {2}}$. Upon exposure to various post-growth thermal treatments these values were found to degrade by up to an order of magnitude, but overall performance still far exceeded the demands for the tandem solar cell operating under AM1.5G, with further extension to operation under medium to high concentration possible.