Epitaxial growth of InGaAs on MgAl2O4 spinel for one-sun photovoltaics

We demonstrate coincident-site lattice-matched growth of InGaAs layers on (001) MgAl2O4 spinel substrates, using a 45° rotation between the lattices, by molecular beam epitaxy. This is the first step towards easily removable multijunction solar cells with inert, reusable substrates. High-resolution cross-sectional transmission electron microscopy (TEM) measurements indicate that microtwins originate at the InGaAs/spinel interface, but tend to annihilate leaving the upper parts of layers relatively twin-free. Plan-view TEM indicates a high density of threading dislocations. InGaAs layers grown at elevated temperatures show improved transport properties, with majority-carrier mobilities approaching typical values for homoepitaxial GaAs on GaAs substrates. Simple p–i–n junctions show photovoltaic efficiencies above 1%.

► Lattice-matched InGaAs growth by molecular beam epitaxy.
► Coincident-site lattice match of InGaAs to MgAl2O4 substrates.
► High density of planar defects but good overall material quality.
► Working lattice-matched InGaAs solar cell on oxide substrate.