Initiation strategies for simultaneous control of antiphase domains and stacking faults in GaAs solar cells on Ge
Incorporating a Ge junction into a lattice matched GaInP/GaAs/GaInNAsSb triple junction cell grown by molecular beam epitaxy (MBE) could enable concentrated efficiencies of ~50% Epitaxial integration allows lift off and wafer bonding steps to be avoided, but growth of III Vs on Ge by MBE can lead to antiphase domains (APD) and stacking fault pyramids (SFP) both of which diminish solar cell performance. Initiating growth by migration enhanced epitaxy (MEE) is typically cited as necessary to obtain high quality III Vs on Ge. In this work, the authors show that typical MEE growth conditions force a compromise between APD height (hAPD) and SFP density (rSFP) As APDs can readily self terminate while SFPs cannot, a two step initiation strategy was employed, where MEE is performed under conditions that minimize rSFP followed by low temperature MBE conditions that encourage APD termination. By doing so, the authors obtained rSFP 104 cm 2 with hAPD 57 nm. The authors also demonstrated that high quality GaAs.