InAlAs solar cells grown by alternative MOVPE precursors

Epitaxial layers of InAlAs are potential candidates for the top cell in triple-junction photovoltaics on InP. Growth conditions during metalorganic vapor phase epitaxy (MOVPE) of InAlAs affect the material properties and subsequently the device characteristics of the epilayers. Material development of InAlAs lattice-matched to InP using trimethylaluminum (TMAl) and tritertiarybutyl aluminum (TTBAl) is compared. Furthermore, InAlAs development using TTBAl is compared in conjunction with either arsine or tertiarybutylarsine (TBAs). Identical devices were grown from each aluminum source and are fabricated in parallel. The TTBAl/TBAs-InAlAs may have degraded during growth due to gas phase pre-reactions and resulted in a 6% efficient cell. However, using arsine, the TMAl-InAlAs devices showed maximum efficiency of 11.5% under 1-sun AM1.5, while TTBAl-InAlAs devices showed 12% (both without anti-reflective coatings). Dark current-voltage measurements of TMAl-InAlAs indicate higher material quality, though TTBAl-InAlAs has greater spectral response.