Marked enhancement in the efficiency of deep ultraviolet light-emitting diodes by using a Al x Ga1-x N carrier reservoir layer

He, Longfei; Zhao, Wei; Zhang, Kang; He, Chenguang; Wu, Hualong; Liu, Xiaoyan; Luo, Xingjun; Li, Shuti; Chen, Zhitao

doi:10.7567/1882-0786/ab22df

Cited by 21 publications

(11 citation statements)

References 29 publications

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“…[24] However, when the QW thickness is at the monolayer level, the localization and overlap of carriers are no longer improved. [45,47] To enhance the carrier overlap, we design staggered MQW as follows: the barrier is 10-nm-thick, the total width of the QW region is 3-ML-thick of whom 2 MLs are the AlGaN insertion layer and 1 ML is the GaN layer. Figure 1 presents the results of calculated carrier localization and wavefunction overlap in the QW region for two kinds of structures with an Al composition of 0% and 60%, respectively.…”

Section: Resultsmentioning

confidence: 99%

“…It is consistent with the theoretically predicted results shown in Figure 1 that the QCSE-induced wavefunction separation between holes and electrons is dominant, which obstructs the recombination of carriers and thus suppresses light emission. The ultra-thin staggered MQWs structure greatly increases the overlap of the electron/hole wavefunctions by reducing QCSE, [44][45][46] meanwhile announcing the benefit of suppressing the conventional carrier injection issue in traditional DUV-LEDs.…”

Section: Resultsmentioning

confidence: 99%

“…In this letter, an ultra-thin AlGaN/GaN staggered QWs structure is proposed to compromise the carrier confinement and electron-hole wavefunction overlap. [44][45][46][47] Benefiting from such a structure, an ultra-high WPE value of 5.25% with an output power of ≈452 mW is achieved in a 2-inch scaled DUVSE at the emission wavelength of 248 nm. Our results announce the prospective of e-beam pumped AlGaN-based wafer-scaled DUVSE, particularly toward the shortage of high dense LED-array based DUV integrated light source.…”

Section: Introductionmentioning

confidence: 99%

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High‐Efficiency E‐Beam Pumped Deep‐Ultraviolet Surface Emitter Based on AlGaN Ultra‐Thin Staggered Quantum Wells

Wang

Yuan

Tao

et al. 2022

Advanced Optical Materials

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lifetime, [1][2][3] high stability, [4] and application flexibility. [5] The ones with an emission wavelength of ≈250 nm exhibit the predominant advantage of sterilization, especially for inactivating Bacillus subtilis spores. [6][7][8] Unfortunately, the LEDs with shorter emission wavelength (≤250 nm) present terrible wall-plug-efficiency (WPE), which is less than 1%, [1][2][3] due to poor hole injection efficiency, [9] strong quantum-confined Stark effect (QCSE), [10][11][12][13][14][15][16] and p-GaN electrode induced UV-absorption. [17][18][19][20][21] Moreover, such low WPE results in a huge amount of heat at a large injection current and hinders the device's reliability, thus obstructing the fabrication of a highpower-density integrated UV light source.In order to disregard the above-mentioned issues, the electron beam-pumped deep-ultraviolet surface emitter (DUVSE) is proposed to increase the output power and avoid the conventional carrier injection layers. [22][23][24][25][26][27][28] The device merely consists of a carbon nanotube (CNT) field emitter and AlGaN multiple quantum wells (MQWs). This DUVSE announces plenty of advantages such as low emitted light re-absorption, [24] simple epitaxial structure, [23] and solo-device fabrication at wafer-scale. [22] In A 2-inch wafer-scale electron-beam (e-beam) pumped deep-ultraviolet surface emitter (DUVSE) with high efficiency and high output power at an emission wavelength of 248 nm is reported. This DUVSE benefits from ultra-thin staggered AlN/AlGaN/GaN multiple quantum wells (MQWs), which compromise the electron-hole overlap and carrier confinement and thus significantly improve the emission efficiency. The wall-plug-efficiency (WPE) is increased by six times to 5.25% in comparison to that of conventional DUV lightemitting devices (LEDs) based on AlGaN MQWs. This WPE is achieved under an anode voltage and current of 8 kV and 1 mA, where the output power is 420 mW. This output power can be further enhanced to 702 mW by increasing the anode current to 3 mA. The enhanced WPE and uniform electron beam distribution lighten the avenue to achieve a wafer-scale high power dense DUV light source, which is a challenge for conventional DUV-LEDs, in particular with an emission wavelength of less than 250 nm.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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High‐Efficiency E‐Beam Pumped Deep‐Ultraviolet Surface Emitter Based on AlGaN Ultra‐Thin Staggered Quantum Wells

Wang

Yuan

Tao

et al. 2022

Advanced Optical Materials

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“…To overcome this challenge, some designs have been proposed, e.g. optimization of quantum well (QW) width [13], staggered QWs [14], gradually increased quantum barrier (QB) thickness [11], graded QBs [15], graded-Al-composition last QB [16] and proper electron blocking layer (EBL) designs [17][18][19][20]. These methods primarily focus on designing proper active region and p-type EBL to alleviate electron leakage into the p-type layer and enhance hole injection into active region.…”

Section: Introductionmentioning

confidence: 99%

Introducing an n-type electron deceleration layer to enhance the luminous efficiency of AlGaN-based DUV-LEDs

et al. 2023

Self Cite

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The internal quantum efficiency (IQE) of conventional AlGaN-based deep-ultraviolet (DUV) light-emitting diodes (LEDs) is seriously limited by the poor and inhomogeneous carrier injection. The typical solution is to optimize the structure parameters of p-type region and active region. In this work, however, we try to address this issue by introducing an n-type electron deceleration layer (EDL) underneath multiple quantum wells (MQWs). On one hand, the electron deceleration layer helps to decrease the electron velocity and thus increase the electron capture rate. On the other hand, it can also reduce barrier heights in the band valence and thus enhance the hole transport in the multiple quantum wells. As a consequence, the concentrations of electrons and holes in the multiple quantum wells were significantly increased, resulting in the enhancement of radiative recombination. Compared to the conventional structure, the DUV-LED structure with an electron deceleration layer achieves a higher internal quantum efficiency, leading to a 39% improvement in the light output power. It is believed that performing energy-band engineering in n-type region has great application prospects for high-performance DUV-LEDs.

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mentioning

confidence: 99%

Effect of a Lateral Overgrowth Process on the Strain Evolution of AlN Films Grown on a Nanopatterned Sapphire Substrate for Ultraviolet‐C Light‐Emitting Diode Applications

Liu

Hoo

Chen

et al. 2021

Physica Rapid Research Ltrs

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Ultraviolet-C (UVC) light-emitting diodes (LEDs) based on AlGaN have been confirmed as an excellent potential candidate for various sterilization applications such as water/air purification, medical diagnostics, security, and so on. [1][2][3][4][5] In particular, the global outbreak of the COVID-19 has sparked even more research enthusiasm to UVC LEDs in both research and industry field due to their superior ability to eliminate severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) within second level. [6] However, in terms of device performance and mass production costs, UVC LEDs are still not comparable with GaN-based blue/green LEDs, and the main challenge is to achieve high crystalline quality and large-size AlN templates. The relatively large mismatch of lattice and thermal expansion between AlN and sapphire substrates results in the generation of numerous dislocations whose density is up to 10 10 cm À2 at the AlN/sapphire interface, which intensively affects the radiative property and reliability of UVC LEDs. [7,8] However, to realize high-performance UVC LED devices, AlN templates with threading dislocation (TD) density below 10 9 cm À2 are preferred. [1] To address this problem, epitaxial lateral overgrowth (ELOG) was proposed through the use of nanopatterned sapphire substrates (NPSSs), which subsequently became widespread due to the successful annihilation of TDs to %10 8 cm À2 . To further investigate the contribution of ELOG, NPSSs with various types of patterns were designed to eliminate dislocations. [9] Although the crystal quality has satisfied the subsequent requirements for epitaxy, the residual strain of the AlN template on NPSS is also quite important, because it greatly affects the warpage of wafer: excessive warpage leads to surface cracks and damages the uniformity of the chips on wafer. Previous studies have found that AlN on NPSS with hole-type pattern presents tensile strain which causes horrendous cracks. [10,11] In addition, the strain state also affects the surface roughness and the relaxation ratio of the upper AlGaN layer, which is accompanied by freshly generated dislocations. Thus, it is meaningful to understand how the NPSS pattern affects the strain evolution and further contributes to UVC LED light emission, which is crucial to optimizing device performance by modulating NPSS patterns.In this work, strain evolution of AlN templates grown on two types of NPSSs (hole type [HT] and pillar type [PT], respectively) is investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD) reciprocal space map (RSM). It was found that the crystal merging of the AlN on HT-NPSS during ELOG leads to tensile strain, whereas the AlN on PT-NPSS, in which there is

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Marked enhancement in the efficiency of deep ultraviolet light-emitting diodes by using a Al_xGa_1-xN carrier reservoir layer

Cited by 21 publications

References 29 publications

High‐Efficiency E‐Beam Pumped Deep‐Ultraviolet Surface Emitter Based on AlGaN Ultra‐Thin Staggered Quantum Wells

High‐Efficiency E‐Beam Pumped Deep‐Ultraviolet Surface Emitter Based on AlGaN Ultra‐Thin Staggered Quantum Wells

Introducing an n-type electron deceleration layer to enhance the luminous efficiency of AlGaN-based DUV-LEDs

Effect of a Lateral Overgrowth Process on the Strain Evolution of AlN Films Grown on a Nanopatterned Sapphire Substrate for Ultraviolet‐C Light‐Emitting Diode Applications

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