Effect of Varying Three-Dimensional Strain on the Emission Properties of Light-Emitting Diodes Based on (In,Ga)N/GaN Nanowires

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

Electroluminescence and current–voltage measurements of single-(In,Ga)N/GaN-nanowire light-emitting diodes in a nanowire ensemble

“…Note that for the low-current regime, the contribution of emission line 3, which is only well identifiable for currents higher than 200 nA, might be hidden in line 2. We note that the similarity between the line analysis in [7] and the data presented here corroborates our assumption that spectrum C corresponds to a single contacted NW.…”

“…The individual spectra consist of three emission lines, the intensity of which changes in a characteristic way with current. This phenomenon is caused by the N polarity of the NWs and the three-dimensional strain profile resulting from elastic relaxation at the free sidewall surfaces, as previously shown in [7].…”

“…More importantly, information about the actual current density in the semiconductor heterostructure is crucial for a meaningful assessment of NW-ensemble devices, in particular in comparison with planar devices. This information is equally decisive for the comparison of device simulations as reported in [7] with experimental results for NW LEDs. Therefore, the measurement technique employed here is a very powerful analysis tool for the investigation of LEDs based on NW ensembles and provides new opportunities for their detailed study.…”

Electron Transport Properties of AlxGa1−xN/GaN Transistors Based on

“…The high peak velocity (2.5×10 7 cm/s) and saturation velocity (1.3×10 7 cm/s) permit fast transit times and high-frequency amplifiers. There are also promising applications to blue light emitting diodes [4,5,10] and ultraviolet avalanche photodiodes [11].…”

Realization of Wurtzite GaSb Using InAs Nanowire Templates

“…Depending on how the secondary material is accommodated on the initial, the coherence between the crystal structures of the two may be influenced, giving rise to potential misfit dislocations or strain in the vicinity of the heterointerface . Such aspects can significantly affect the physical properties of the heterostructures . Additionally, any intermixing of the two compounds or interdiffusion of elements, even at the atomic scale, can have a large impact on the properties of the heterostructures and hence the performance of any device based on them Therefore, it is of high importance to study the interfaces at the atomic scale.…”