3 years ago

Time-resolved photoluminescence characterization of GaAs nanowire arrays on native substrate.

Xulu Zeng, Wei Zhang, Gaute Otnes, Vilgailė Dagytė, Magnus Heurlin, Nicklas Anttu, Magnus T Borgstrom, Enrique Barrigón
Time-resolved photoluminescence (TRPL) measurements of nanowires are often carried out on broken-off nanowires in order to avoid the ensemble effects as well as substrate contribution. However, the development of nanowire-array solar cells could benefit from non-destructive optical characterization to allow faster feedback and further device processing. With this work, we show that different nanowire array and substrate spectral behaviors with delay time and excitation power can be used to determine which part of the sample dominates the detected spectrum. Here, we evaluate TRPL characterization of dense periodic as-grown GaAs nanowire arrays on a p-type GaAs substrate, including a sample with uncapped GaAs nanowires and several samples passivated with AlGaAs radial shell of varied composition and thickness. We observe a strong spectral overlap of substrate and nanowire signals and find that the nanowires can absorb part of the substrate luminescence signal, thus resulting in a modified substrate signal. The level of absorption depends on the nanowire-array geometry, making a deconvolution of the nanowire signal very difficult. By studying TRPL of substrate-only and as-grown nanowires at 770 nm and 400 nm excitation wavelengths, we find a difference in spectral behavior with delay time and excitation power that can be used to assess whether the signal is dominated by the nanowires. We find that the nanowire signal dominates with 400 nm excitation wavelength, where we observe two different types of excitation power dependence for the nanowires capped with high and low Al composition shells. Finally, from the excitation power dependence of the peak TRPL signal, we extract an estimate of background carrier concentration in the nanowires.

Publisher URL: http://doi.org/10.1088/1361-6528/aa974b

DOI: 10.1088/1361-6528/aa974b

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