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Carrier Recombination in Highly Uniform and Phase-Pure GaAs/(Al,Ga)As Core/Shell Nanowire Arrays on Si(111): Implications for Light-Emitting Devices

GaAs-based nanowires are among the most promising candidates for realizing a monolithic integration of III-V optoelectronics on the Si platform. To realize their full potential for applications as light absorbers and emitters, it is crucial to understand their interaction with light governing the absorption and extraction efficiency, as well as the carrier recombination dynamics determining the radiative efficiency. Here, we study the spontaneous emission of zincblende GaAs/(Al,Ga)As core/shell nanowire arrays by µ-photoluminescence spectroscopy. These ordered arrays are synthesized on patterned Si(111) substrates using molecular beam epitaxy, and exhibit an exceptionally low degree of polytypism for interwire separations exceeding a critical value. We record emission spectra over more than five orders of excitation density for both steady-state and pulsed excitation to identify the nature of the recombination channels. An abrupt Mott transition from excitonic to electron-hole-plasma recombination is observed, and the corresponding Mott density is derived. Combining these experiments with simulations and additional direct measurements of the external quantum efficiency using a perfect diffuse reflector as reference, we are able to extract the internal quantum efficiency as a function of carrier density and temperature as well as the extraction efficiency of the nanowire array. The results vividly document the high potential of GaAs/(Al,Ga)As core/shell nanowires for efficient light emitters integrated on the Si platform. Furthermore, the methodology established in this work can be applied to nanowires of other materials systems of interest for optoelectronic applications.

Left: Bird’s eye (15°) view secondary electron micrograph of an ordered GaAs/(Al,Ga)As core/shell nanowire array with a pitch of 700 nm. Right: Low-temperature (10 K) µ-photoluminescence spectra of the same nanowire field recorded with increasing generation rate G as indicated by the arrow. The nature of the two main lines in the spectra is indicated in the figure. The inset shows the dependence of the internal and external quantum efficiencies on G. The symbols represent experimental data, while the line shows a best fit of a rate equation model taking into account the main recombination channels in the nanowires. The sketch summarizes the structure of the sample.

Author: Miriam Oliva, Timur Flissikowski, Michał Góra, Jonas Lähnemann, Jesús Herranz, Ryan B. Lewis, Oliver Marquardt, Manfred Ramsteiner, Lutz Geelhaar, and Oliver Brandt
Title: Carrier Recombination in Highly Uniform and Phase-Pure GaAs/(Al,Ga)As Core/Shell Nanowire Arrays on Si(111): Implications for Light-Emitting Devices
Source: ACS Appl. Nano Mater. 6, 15278–15293 (2023) 
DOI: 10.1021/acsanm.3c03242