Search

Semipolar {101¯1} InGaN quantum dots (QDs) formed on GaN V‐shaped pits by metal–organic vapor‐phase epitaxy (MOVPE) with a growth interruption method are reported. The 3D GaN V‐pit structures are directly grown on a patterned sapphire substrate (PSS). By adjusting the pattern arrangement direction on the substrate, it is observed in the scanning electron microscopy (SEM) image that elliptical QDs are formed on the {101¯1} semipolar sidewalls of the V‐pits with a density of about 5 × 1010 cm−2. The emission wavelength of semipolar InGaN QDs is confirmed by cathodoluminescence (CL). The gradient distribution of In composition and QD size are observed along the sidewall of the V‐pits. On this basis, a three‐period semipolar InGaN QD sample is prepared. For the temperature‐dependent photoluminescence (TDPL) test, the prominent peak of the sample shows a blueshift with the increase in temperature and reaches the green band (≈523 nm) at room temperature (RT). According to time‐resolved photoluminescence (TRPL) decay curves, a carrier lifetime of 329.3 ps fit by the stretched exponential model is obtained at RT. Compared with c‐plane QDs with the same growth method, the semipolar QDs have a shorter radiative recombination lifetime due to suppressed polarization electric field. [ABSTRACT FROM AUTHOR]

Micro‐LEDs are regarded as ideal light sources for next‐generation display and high‐speed visible‐light communication (VLC). However, the conventional micro‐LEDs based on InGaN quantum well (QW) active region suffer from a low efficiency under small injection (below 1 A cm−2) due to the size‐dependent effect and a limited 3 dB bandwidth (hundreds of MHz) due to quantum‐confined Stark effect. Here, InGaN quantum dots (QDs) are proposed as the active region of micro‐LEDs to address these challenges for their strong localization and low‐strain features. Green InGaN QDs are self‐assembled under Stranski–Krastanov (SK) and Volmer–Weber (VW) modes by using metal organic vapor phase epitaxy. The SK QDs can shift the peak efficiency of a micro‐LED to an extremely low current density of 0.5 A cm−2 (almost two orders of magnitude lower compared to QW ones) with an external quantum efficiency of 18.2% (nearly two times higher than present green micro‐LEDs). Besides, green micro‐LEDs based on VW QDs reach a 3 dB bandwidth of 1.3 GHz. These results indicate that InGaN QDs can provide an ultimate solution to micro‐LEDs for display and VLC applications, especially since they are fully compatible with current light‐emitting diode (LED) industrial technology. [ABSTRACT FROM AUTHOR]

GaN quantum dots embedded in nanowires have attracted much attention due to their superior optical properties. However, due to the large surface-to-volume ratio of the nanowire, the impacts of surface states are the primary issue responsible for the degradation of internal quantum efficiency (IQE) in heterostructured dot-in-nanowires. In this paper, we investigate the carrier recombination mechanism of GaN/AlN dot-in-nanowires with an in situ grown AlN shell structure. Ultraviolet photoelectron spectroscopy (UPS) measurements were performed to describe the band bending effect on samples with different shell thicknesses. Temperature-dependent photoluminescence (TDPL) data support that increasing the AlN shell thickness is an efficient way to improve internal quantum efficiency. Detailed carrier dynamics was analyzed and combined with time-resolved photoluminescence (TRPL). The experimental data are consistent with our physical model that the AlN shell can effectively flatten the band bending near the surface and isolate the surface non-radiative recombination center. Our systematic research on GaN/AlN quantum dots in nanowires with a core–shell structure may significantly advance the development of a broad range of nanowire-based optoelectronic devices. [ABSTRACT FROM AUTHOR]

The dislocations in InGaN/GaN quantum dots grown by metal organic chemical vapor deposition were studied by high-resolution transmission electron microscopy combining the Fourier filtering process. The misfit dislocations were observed in uncapped InGaN/GaN quantum dots. However, for the capped InGaN/GaN quantum dots, the GaN capping layer was found to suppress the generation of misfit dislocations and hence hindered the strain relaxation. Therefore, an overgrowth InGaN layer was used to relieve the strain in InGaN quantum dots and misfit dislocations were correspondingly found in these samples. In addition, defects were observed in low temperature GaN layers which suggested the existence of stacking faults. [ABSTRACT FROM AUTHOR]