Plasmon Enhanced Internal Quantum Efficiency of CdSe/ZnS Quantum Dots

AlGaN based light emitting diodes (LEDs) will play a key role for the development of applications in the ultra-violet (UV). In the UVB region (280–320 nm), phototherapy and plant lighting are among the targeted uses. However, UVB LED performances still need to be improved to reach commercial markets. In particular, the design and the fabrication process of the active region are central elements that affect the LED internal quantum efficiency (IQE). We propose the use of nanometer-sized epitaxial islands (i.e., so called quantum dots (QDs)) to enhance the carrier localization and improve the IQE of molecular beam epitaxy (MBE) grown UVB LEDs using sapphire substrates with thin sub-µm AlN templates. Taking advantage of the epitaxial stress, AlGaN QDs with nanometer-sized (≤10 nm) lateral and vertical dimensions have been grown by MBE. The IQE of the QDs has been deduced from temperature dependent and time resolved photoluminescence measurements. Room temperature IQE values around 5 to 10% have been found in the 290–320 nm range. QD-based UVB LEDs were then fabricated and characterized by electrical and electroluminescence measurements. On-wafer measurements showed optical powers up to 0.25 mW with external quantum efficiency (EQE) values around 0.1% in the 305–320 nm range.

Download Full-text

Enhancement of carrier localization effect and internal quantum efficiency through In-rich InGaN quantum dots

Superlattices and Microstructures ◽

10.1016/j.spmi.2017.11.026 ◽

2018 ◽

Vol 113 ◽

pp. 497-501 ◽

Cited By ~ 7

Author(s):

Jianjie Liu ◽

Zhigang Jia ◽

Shufang Ma ◽

Hailiang Dong ◽

Guangmei Zhai ◽

...

Keyword(s):

Quantum Dots ◽

Quantum Efficiency ◽

Internal Quantum Efficiency ◽

Carrier Localization ◽

Localization Effect

Download Full-text

Improving the internal quantum efficiency of green InGaN quantum dots through coupled InGaN/GaN quantum well and quantum dot structure

Applied Physics Express ◽

10.7567/apex.8.094001 ◽

2015 ◽

Vol 8 (9) ◽

pp. 094001 ◽

Cited By ~ 6

Author(s):

Jiadong Yu ◽

Lai Wang ◽

Di Yang ◽

Zhibiao Hao ◽

Yi Luo ◽

...

Keyword(s):

Quantum Dots ◽

Quantum Dot ◽

Quantum Well ◽

Quantum Efficiency ◽

Internal Quantum Efficiency

Download Full-text

Studies on Carrier Recombination in GaN/AlN Quantum Dots in Nanowires with a Core–Shell Structure

Nanomaterials ◽

10.3390/nano10112299 ◽

2020 ◽

Vol 10 (11) ◽

pp. 2299

Author(s):

Jun Deng ◽

Zhibiao Hao ◽

Lai Wang ◽

Jiadong Yu ◽

Jian Wang ◽

...

Keyword(s):

Quantum Dots ◽

Quantum Efficiency ◽

Shell Structure ◽

Internal Quantum Efficiency ◽

Systematic Research ◽

Core Shell ◽

Band Bending ◽

Recombination Mechanism ◽

Carrier Recombination ◽

Core Shell Structure

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.

Download Full-text

Perspectives on UVC LED: Its Progress and Application

Photonics ◽

10.3390/photonics8060196 ◽

2021 ◽

Vol 8 (6) ◽

pp. 196

Author(s):

Tsung-Chi Hsu ◽

Yu-Tsai Teng ◽

Yen-Wei Yeh ◽

Xiaotong Fan ◽

Kuo-Hsiung Chu ◽

...

Keyword(s):

Quantum Efficiency ◽

Flip Chip ◽

Layer Structure ◽

Light Emitting Diode ◽

Internal Quantum Efficiency ◽

Reverse Current ◽

Light Extraction ◽

Epitaxial Layers ◽

High Electron ◽

Recombination Rates

High-quality epitaxial layers are directly related to internal quantum efficiency. The methods used to design such epitaxial layers are reviewed in this article. The ultraviolet C (UVC) light-emitting diode (LED) epitaxial layer structure exhibits electron leakage; therefore, many research groups have proposed the design of blocking layers and carrier transportation to generate high electron–hole recombination rates. This also aids in increasing the internal quantum efficiency. The cap layer, p-GaN, exhibits high absorption in deep UV radiation; thus, a small thickness is usually chosen. Flip chip design is more popular for such devices in the UV band, and the main factors for consideration are light extraction and heat transportation. However, the choice of encapsulation materials is important, because unsuitable encapsulation materials will be degraded by ultraviolet light irradiation. A suitable package design can account for light extraction and heat transportation. Finally, an atomic layer deposition Al2O3 film has been proposed as a mesa passivation layer. It can provide a low reverse current leakage. Moreover, it can help increase the quantum efficiency, enhance the moisture resistance, and improve reliability. UVC LED applications can be used in sterilization, water purification, air purification, and medical and military fields.

Download Full-text