In the experimental electroluminescence (EL) spectra of light-emitting diodes (LEDs) based on N-polar (In,Ga)N/GaN nanowires (NWs), we observe a double-peak structure. The relative intensity of the two peaks evolves in a peculiar way with injected current. Spatially and spectrally resolved EL maps confirm the presence of two main transitions in the spectra and suggest that they are emitted by a majority of the single nano LEDs. In order to elucidate the physical origin of this effect, we perform theoretical calculations of the strain, electric field, and charge-density distributions for both planar LEDs and NW LEDs. On this basis, we simulate also the EL spectra of these devices, which exhibit a double-peak structure for N-polar heterostructures, in both the NW and the planar case. By contrast, this feature is not observed when Ga-polar planar LEDs are simulated. We find that the physical origin of the double-peak structure is a stronger quantum-confined Stark effect occurring in the first and last quantum well of the N-polar heterostructures. The peculiar evolution of the relative peak intensities with injected current, seen only in the case of the NW LED, is attributed to the three-dimensional strain variation resulting from elastic relaxation at the free sidewalls of the NWs. Therefore, this study provides important insights on the working principle of N-polar LEDs based on both planar and NW heterostructures.
Effect of Varying Three-Dimensional Strain on the Emission Properties of Light-Emitting Diodes Based on (In,Ga)N/GaN Nanowires
De Santi, C.;Meneghini, M.;Zanoni, E.
2017
Abstract
In the experimental electroluminescence (EL) spectra of light-emitting diodes (LEDs) based on N-polar (In,Ga)N/GaN nanowires (NWs), we observe a double-peak structure. The relative intensity of the two peaks evolves in a peculiar way with injected current. Spatially and spectrally resolved EL maps confirm the presence of two main transitions in the spectra and suggest that they are emitted by a majority of the single nano LEDs. In order to elucidate the physical origin of this effect, we perform theoretical calculations of the strain, electric field, and charge-density distributions for both planar LEDs and NW LEDs. On this basis, we simulate also the EL spectra of these devices, which exhibit a double-peak structure for N-polar heterostructures, in both the NW and the planar case. By contrast, this feature is not observed when Ga-polar planar LEDs are simulated. We find that the physical origin of the double-peak structure is a stronger quantum-confined Stark effect occurring in the first and last quantum well of the N-polar heterostructures. The peculiar evolution of the relative peak intensities with injected current, seen only in the case of the NW LED, is attributed to the three-dimensional strain variation resulting from elastic relaxation at the free sidewalls of the NWs. Therefore, this study provides important insights on the working principle of N-polar LEDs based on both planar and NW heterostructures.
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