Ultrashort carrier lifetime of vapor–liquid–solid-grown GaN/InGaN multi-quantum-well coaxial nanorods

We report on the demonstration of a new type of axial nanowire LED heterostructures, with the use of self-organized InGaN/AlGaN dot-in-a-wire core-shell nanowire arrays. The large bandgap AlGaN shell is spontaneously formed on the sidewall of the nanowire during the growth of AlGaN barrier of the quantum dot active region. As such, nonradiative surface recombination, that dominates the carrier dynamics of conventional axial nanowire LED structures, can be largely eliminated, leading to significantly increased carrier lifetime from ~0.3 ns to 4.5 ns. The luminescence emission is also enhanced by orders of magnitude. Moreover, the p-doped AlGaN barrier layers can function as distributed electron blocking layers (EBLs), which is found to be more effective in reducing electron overflow, compared to the conventional AlGaN EBL. The device displays strong white-light emission, with a color rendering index of ~95. An output power of >5 mW is measured for a 1 mm × 1 mm device, which is more than 500 times stronger than the conventional InGaN axial nanowire LEDs without AlGaN distributed EBLs.

Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

Engineering the Carrier Dynamics of InGaN Nanowire White Light-Emitting Diodes by Distributed p-AlGaN Electron Blocking Layers

Nguyen

Djavid

Woo

et al. 2015

“…To study the carrier dynamic in details, the PL decay curves have been fitted by using the stretched exponential function: where β is the stretching parameter and I(t) is the time-dependent PL intensity 51 . The stretching parameter β was concerned by localized states in the QW, and is closely related to the crystalline quality 52 . All parameters extracted from the fitting process are presented in Table 1 .…”

Section: Resultsmentioning

confidence: 99%

Carrier localization in In-rich InGaN/GaN multiple quantum wells for green light-emitting diodes

Jeong

et al. 2015

Carrier localization phenomena in indium-rich InGaN/GaN multiple quantum wells (MQWs) grown on sapphire and GaN substrates were investigated. Temperature-dependent photoluminescence (PL) spectroscopy, ultraviolet near-field scanning optical microscopy (NSOM), and confocal time-resolved PL (TRPL) spectroscopy were employed to verify the correlation between carrier localization and crystal quality. From the spatially resolved PL measurements, we observed that the distribution and shape of luminescent clusters, which were known as an outcome of the carrier localization, are strongly affected by the crystalline quality. Spectroscopic analysis of the NSOM signal shows that carrier localization of MQWs with low crystalline quality is different from that of MQWs with high crystalline quality. This interrelation between carrier localization and crystal quality is well supported by confocal TRPL results.

“…Both UIF and EIF samples grown at 710 °C exhibited two-peak decay, i.e., high energy (blue) and low energy (green) decays. This behaviour can be attributed to the spatial fluctuation of In concentration along the axis of the InGaN NWs, which can lead to the formation of shallow (high energy) and deep (low energy) recombination centers 26 27 28 . The carrier recombination in the UIF sample mostly occurred through the deeply localized states, which showed a higher PL emission intensity than the shallow localized states, suggesting a high degree of In fluctuation.…”

Section: Resultsmentioning

confidence: 99%

Vertically aligned InGaN nanowires with engineered axial In composition for highly efficient visible light emission

ElKabbash

Kang

Yoo

et al. 2015

Self Cite

We report on the fabrication of novel InGaN nanowires (NWs) with improved crystalline quality and high radiative efficiency for applications as nanoscale visible light emitters. Pristine InGaN NWs grown under a uniform In/Ga molar flow ratio (UIF) exhibited multi-peak white-like emission and a high density of dislocation-like defects. A phase separation and broad emission with non-uniform luminescent clusters were also observed for a single UIF NW investigated by spatially resolved cathodoluminescence. Hence, we proposed a simple approach based on engineering the axial In content by increasing the In/Ga molar flow ratio at the end of NW growth. This new approach yielded samples with a high luminescence intensity, a narrow emission spectrum, and enhanced crystalline quality. Using time-resolved photoluminescence spectroscopy, the UIF NWs exhibited a long radiative recombination time (τr) and low internal quantum efficiency (IQE) due to strong exciton localization and carrier trapping in defect states. In contrast, NWs with engineered In content demonstrated three times higher IQE and a much shorter τr due to mitigated In fluctuation and improved crystal quality.