Molecular beam epitaxy of InAlAsSb for the top cell in high-efficiency InP-based lattice-matched triple-junction solar cells

Triple-junction solar cells lattice-matched to InP have recently gained interest as an alternative to traditional GaAs-based devices. We predict a 1.74, 1.17, 0.70 eV device can attain high efficiency and can be achieved lattice-matched to InP. However, InAlAsSb, a relatively immature material, is required for the top junction. Here, we performed a systematic study of the substrate temperature and group-V overpressure of (In
_0.52
Al
_0.48
As)
_0.6
(AlAs
_0.56
Sb
_0.44
)
_0.4
. We found that the peak PL emission energy blue-shifted as the substrate temperature decreased and as the group-V overpressure increased, implying that low adatom mobility is key to attaining InAlAsSb with the expected bandgap energy.