Core–shell nanowires (NW)
have become very prominent systems for band engineered NW heterostructures
that effectively suppress detrimental surface states and improve performance
of related devices. This concept is particularly attractive for material
systems with high intrinsic surface state densities, such as the low-bandgap
In-containing group-III arsenides, however selection of inappropriate,
lattice-mismatched shell materials have frequently caused undesired
strain accumulation, defect formation, and modifications of the electronic
band structure. Here, we demonstrate the realization of closely lattice-matched
radial InGaAs–InAlAs core–shell NWs tunable over large
compositional ranges [x(Ga)∼y(Al) = 0.2–0.65] via completely catalyst-free selective-area
molecular beam epitaxy. On the basis of high-resolution X-ray reciprocal
space maps the strain in the NW core is found to be insignificant
(ε < 0.1%), which is further reflected by the absence of
strain-induced spectral shifts in luminescence spectra and nearly
unmodified band structure. Remarkably, the lattice-matched InAlAs
shell strongly enhances the optical efficiency by up to 2 orders of
magnitude, where the efficiency enhancement scales directly with increasing
band offset as both Ga- and Al-contents increase. Ultimately, we fabricated
vertical InGaAs−InAlAs NW/Si photovoltaic cells and show that
the enhanced internal quantum efficiency is directly translated to
an energy conversion efficiency that is ∼3–4 times larger
as compared to an unpassivated cell. These results highlight the promising
performance of lattice-matched III–V core–shell NW heterostructures
with significant impact on future development of related nanophotonic
and electronic devices.