Spectrally-resolved internal quantum efficiency and carrier dynamics of semipolar $(10\bar{1}1)$ core-shell triangular nanostripe GaN/InGaN LEDs

Abstract

We investigate the spectrally resolved internal quantum efficiency (IQE) and carrier dynamics in semipolar [Formula: see text] core-shell triangular nanostripe light-emitting diodes (TLEDs) using temperature-dependent photoluminescence (TDPL) and time-resolved photoluminescence (TRPL) at various excitation energy densities. Using electroluminescence, photoluminescence, and cathodoluminescence measurements, we verify the origins of the broad emission spectra from the nanostructures and confirm that localized regions of high-indium-content InGaN exist along the apex of the nanostructures. Spectrally resolved IQE measurements are then performed, with the spectra integrated from 400-450 nm and 450-500 nm to obtain the IQE of the QWs mainly near the sidewalls and apex of the TLEDs, respectively. TDPL and TRPL are used to decouple the radiative and non-radiative carrier lifetimes for different regions of the emission spectra. We observe that the IQE is higher for the spectral region between 450 nm and 500 nm compared to the IQE between 400 and 450 nm. This result is in contrast to the typical observation that the IQE of planar GaN-based LEDs is lower for longer wavelengths (i.e., higher indium contents). We also observe a longer non-radiative recombination lifetime for the longer wavelength portion of the spectrum. Several explanations are proposed for the improved IQE and longer non-radiative lifetime observed near the apex of the nanostructures. The results show that nanostructures may be leveraged to design more efficient green LEDs, potentially addressing a long-standing challenge in GaN-based materials.

A Decade of Nonpolar and Semipolar III-Nitrides: A Review of Successes and Challenges

“…There are many advantages that core‐shell nanostructures may offer in addition to access to polarization‐free material in the nonpolar and semipolar planes. Nanostructures, including triangular nanostripes (Figure a,b), nanowalls (Figure c), and nanowires (Figure d), provide nonpolar and semipolar planes without the need for costly substrate preparations. On the other hand, nanostructure approaches typically require a crystal re‐growth step.…”

“…Furthermore, due to the relaxation of compressive strain in nanostructures, the indium incorporation efficiency may be enhanced and thus could provide a potential solution for the green gap issue. A higher indium content close to the apex of a triangular nanostructure compared to the sidewalls was observed and attributed to lower growth temperature and lower biaxial strain near the apex of the nanostructures . Non‐uniform emission wavelengths across nanostructures have been reported for various nanostructure geometries, highlighting a key challenge with this approach .…”

Spatially and Time-Resolved Carrier Dynamics in Core–Shell InGaN/GaN Multiple-Quantum Wells on GaN Wire

“…6 Similar values (21−35 ps) have been found for polarization-free InGaN/GaN multiquantum wells (MQWs) wires at 300 K. 7,8 In addition, carrier decay rates that deviate from the single-exponential curves were revealed, 9 indicating multiple carrier localization effects present in core−shell InGaN/GaN heterostructures. 10 While ensembles of wires are often investigated by time-resolved photoluminescence (TRPL), 11,12 to date only little attention has been paid to carrier decay rates in single wires using more sophisticated approaches, like time-resolved cathodoluminescence (TRCL) 13 and ultrafast optical microscopy. 14 Alternatively, scanning near-field optical microscopy (SNOM) equipped with a short-pulsed laser 15 and microelectroluminescence through the probe of scanning tunneling microscopy could be used.…”