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SEM image of Au-catalyzed Ge NWs grown on a Si (111) substrate. Analysis of this image gives an average diameter and length of the Ge NWs of 40 nm and 6.5 μm, respectively.
NIR room-temperature PL signal from (a) bulk Ge and (b) Ge NWs with native oxide. (The fitting and experimental data curves have been intentionally offset along the vertical axis to make them distinguishable.)
(a) NIR room-temperature PL spectra of the Ge NWs, measured after different durations of furnace annealing in oxygen at 220 °C. (b) Integrated PL peak intensities of the Ge NWs as a function of annealing time in oxygen gas, measured at a nominal 300 K.
Germanium oxide chemical states fitting analysis applied to the Ge 3d XPS spectrum of the oxide formed by furnace annealing at 220 °C for (a)1 h and (b) 3 h.
(a) (Left) Ge oxide/Ge interface with both relatively fast interface traps (picoseconds-nanosecond timescale) and slower states (∼seconds timescale) in the oxide; (right) GeO2/Ge interface formed after oxidation annealing of the sample, with a lower density of interface states. Fig. (b) Photoexcited carriers in the Ge band diagram. (Left) non-radiative recombination of the majority of photoexcited carriers occurs via trap levels existing in the bandgap of Ge; (right) radiative recombination of both L-valley and Γ-valley electrons after the interface trap density has been reduced by the formation of GeO2.
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