Figure - available from: Nano Express
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Emission at 300 K from as-grown (gray), plasma-treated (blue) and substrate reference (red) samples (a) shows spectrally resolved peak emission averaged over 10 ps. NW samples scaled by 4x. (b) shows semi-log scale time-resolved photoluminescence and fitting from as-grown and plasma-treated NWs. A substrate is included for reference.
Source publication
We demonstrate a significant improvement in the optical performance of GaAs nanowires achieved using a mixed nitrogen-hydrogen plasma which passivates surface states and reduces the rate of nonradiative recombination. This has been confirmed by time-resolved photoluminescence measurements. At room temperature, the intensity and lifetime of radiativ...
Citations
... Losurdo et al. use N 2 -H 2 and higher (350 C) temperatures and show 3Â PL after one year; 19 André et al. show after 1.5 years of air exposure roughly 4Â cryo-PL improvement in GaAs nanowires annealed at over 500 C, 24 similar results of 5Â PL increase compared to as-grown are from Irish et al., where after 1 year plasma-passivated GaAs (350 C similar to Losurdo et al. 19 ) nanowires were studied. 39 The work with most similar samples and characterizations is from Mehdi et al., 25 where planar GaAs samples were passivated with nitrogen plasma and annealed, then aged for 2 years in air and both PL (upto 15Â enhancement at 5 K) and TRPL (at 5 K) were studied. Mehdi et al. do not get rid of the elemental arsenic with just room-temperature plasma nitridation, but the good results require annealing at 620 C, 25 which also crystallizes the initial amorphous layer to cubic GaN (zincblende) 21 or the hexagonal GaN (wurtzite) 40 depending on plasma conditions. ...
GaAs surfaces require electrical and chemical passivation for semiconductor devices, but in order to have air stable passivation, high temperatures have been previously required in the passivation step. Here, we demonstrate air-stable, ex situ plasma passivation of GaAs using consecutive hydrogen and nitrogen plasmas at room temperature. No pre-clean using deoxidizing wet chemistry or other means is required. The hydrogen plasma step removes surface oxides and As, which leaves a Ga-rich layer that the nitrogen plasma then turns to GaN. The formed GaN layer efficiently passivates the surface. The plasma-passivated GaAs shows upto 5× room-temperature photoluminescence after 1 year, and room-temperature time-resolved photoluminescence demonstrates robust passivation even after 3 years, both comparisons to similarly aged unpassivated GaAs. Atomic force microscopy was used to confirm that the passivated surfaces can be made smooth enough for microelectronic applications. Grazing incidence x-ray diffraction indicated that the nitride films are amorphous, and energy-dispersive x-ray spectroscopy was used to estimate the nitrogen content. We used a common inductively coupled plasma reactive ion etching system for plasma passivation, thus enabling the rapid adoption of this technique.
