Lattice-Matched InGaAs–InAlAs Core–Shell Nanowires with Improved Luminescence and Photoresponse Properties

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.

Impact of Outer Shell Structure and Localization Effects on Charge Carrier Dynamics in GaAs/(In,Ga)As Nanowire Core–Shell Quantum Wells

“…The second channel with meV is more difficult to interpret. The value of the activation energy is about twice as large as those reported for closely lattice‐matched GaAs/(Al,Ga)As and (In,Ga)As/(In,Al)As core–shell NWs, which was speculated to be related to a specific recombination center at the {110} interfaces . In the present case, it seems unlikely that this nonradiative channel is related to an interfacial defect, since we obtain exactly the same value of E 2 for samples with an interface to an outer GaAs or AlAs shell.…”

Analytical description of nanowires. I. Regular cross sections for zincblende and diamond structures

“…Such spectra are sensitive to lattice strain which is a function of the material via the Young's modulus (Elliot, 1998). Changes in compressive or expansive stress were shown to modify the optical response of NWires by photoluminescence (PL) (Tomioka et al, 2011;Joyce et al, 2011;Treu et al, 2015). The growth of monolithic NWires depends critically on balanced stress to avoid stacking faults which cause the electronic properties of the NWire to deteriorate.…”

III–V ternary nanowires on Si substrates: growth, characterization and device applications

“…Generally, the elemental composition of the alloy is determined by the growth conditions and growth methods that are used and can be tuned to great extents by altering the growth parameters. Due to this flexibility that can be approached via the optimization of the growth, ternary NWs have been implemented in multiple applications such as energy harvesting, for example, solar cells [20][21] and water splitting devices. [22] Moreover, they have been used for the realization of lasers [23][24] and LEDs [25][26] with a controlled emission, which is determined by the rational design of the composition of the alloy.…”