Integration of thin Al films on In0.18Ga0.82As metamorphic grade structures for low-cost III- V photovoltaics

In
_0.18
Ga
_0.82
As has a bandgap of 1.16eV, ideal for single-junction devices under moderate solar concentration, and is lattice-matched to Al, an earth-abundant and widely available metal which may potentially be employed as substrate or buffer layer for low-cost III-V photovoltaics. In this paper the feasibility of an heteroepitaxial approach to integrate Al on GaAs via metamorphic In
_0.18
Ga
_0.82
As is discussed. Metal organic chemical vapor deposition delivered unstrained In0.18Ga0.82As templates of high quality but proved to be inadequate to fabricate pure Al layers at least at the temperatures typically used for III-V growth, owing to incorporation of considerable amounts of carbon from the precursors. Ex situ thermal evaporation of the metal was attempted, yielding polycrystalline material without epitaxial registry to the In
_0.18
Ga
_0.82
As template. Detailed characterization of the grown specimens and discussion of the issues faced are presented.