Drastic effect of sequential deposition resulting from flux directionality on the luminescence efficiency of nanowire shells

TL;DR

Sequential flux directionality during nanowire shell growth drastically enhances luminescence efficiency by reducing defects and nonradiative centers, highlighting the importance of growth conditions for nanostructure optoelectronic performance.

Contribution

This study reveals the significant impact of flux sequence in molecular beam epitaxy on nanowire shell luminescence, a factor previously overlooked in nanostructure fabrication.

Findings

Luminescence efficiency more than doubled with sequential flux growth.

No extended defects observed despite efficiency differences.

Sequential growth reduces defect-related nonradiative recombination.

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, i. e. when As and the group-III metals essentially do not impinge at the same time, is more than two 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 materials properties of nanowire shells. We expect that this finding holds also for other alloy nanowire shells.