Drastic Effect of Sequential Deposition Resulting from Flux Directionality on the Luminescence Efficiency of Nanowire Shells

Abstract

Core−shell nanowire heterostructures form the basis for many innovative devices. When compound nanowire shells are grown by directional deposition techniques, the azimuthal position of the sources for the different constituents in the growth reactor, substrate rotation, and nanowire self-shadowing inevitably lead to sequential deposition. Here, we uncover for In 0.15 Ga 0.85 As/GaAs shell quantum wells grown by molecular beam epitaxy a drastic impact of this sequentiality on the luminescence efficiency. The photoluminescence intensity of shell quantum wells grown with a flux sequence corresponding to migration enhanced epitaxy, that is, when As and the group-III metals essentially do not impinge at the same time, is more than 2 orders of magnitude higher than for shell quantum wells prepared with substantially overlapping fluxes. Transmission electron microscopy does not reveal any extended defects explaining this difference. Our analysis of photoluminescence transients shows that co-deposition has two detrimental microscopic effects. First, a higher density of electrically active point defects leads to internal electric fields reducing the electron− hole wave function overlap. Second, more point defects form that act as nonradiative recombination centers. Our study demonstrates that the source arrangement of the growth reactor, which is of mere technical relevance for planar structures, can have drastic consequences for the material properties of nanowire shells. We expect that this finding holds good also for other alloy nanowire shells.

Non-Uniformly Strained Core–Shell InAs/InP Nanowires for Mid-Infrared Photonic Applications

“…SEM images of core–shell InAs/InP NW arrays presented in Figure c,d reveal that core–shell NWs are bent in random directions. We assume that both the asymmetry of the MBE chamber (i.e., the group-V and group-III cells are azimuthally arranged opposed to each, and thus, In and P 2 molecular beam fluxes do not impinge on a NW sidewall facet at the same time) or effects of shadowing of randomly positioned NWs can lead to an inhomogeneous shell growth around the NW circumference. , As a result, a lattice mismatch-induced strain from the compressive InP shell leads to the NW bending toward the side with the largest thickness of the shell layer.…”