Abstract
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.
Highlights
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
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
Summary
A major limitation of the high surface-to-volume NWs is their susceptibility to detrimental surface states under ambient conditions. Contrast intensity ratios in the STEM/HAADF image We note that such segregation effect is commonly observed in Alcontaining shells of typical III−V semiconductor core−shell NWs (e.g., GaAs−AlGaAs, GaAs−AlInP, and so forth21,43), which arises from the formation of {112}-oriented nanofacets during shell growth.[21] Overall, the microstructure of the InGaAs−InAlAs core−shell NWs exhibits the common disordered layer stacking of catalyst-free grown InGaAs NWs as well as inclusions of wurtzite (WZ) segments when the InGaAs composition is tuned across the In-rich side[19] (not shown). We treat the measured lattice parameters as hexagonal a (perpendicular to growth direction) and c
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
