Temperature-dependent electroluminescence of stressed and unstressed InAlGaN multi-quantum well UVB LEDs

Höpfner, J.; Gupta, Priti; Guttmann, Martin; Ruschel, Jan; Glaab, Johannes; Kolbe, Tim; Raß, Jens; Knauer, A.; Stölmacker, Christoph; Einfeldt, S.; Wernicke, Tim; Weyers, M.; Kneissl, Michael

doi:10.1063/5.0139200

Cited by 6 publications

(2 citation statements)

References 26 publications

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“…Moreover, doping in the cladding layers indirectly influences the LEE in UV-LEDs. Specifically, owing to the lack of a thorough solution for p-type doping in Al-rich AlGaN, a thick p-GaN layer is widely adopted as a substitute [25,27,33,37,39,41,43] . Hence, the vast majority of the UV light emitted towards the p-region is absorbed, restricting the increase of LEE as well as WPE.…”

Section: Introductionmentioning

confidence: 99%

Progress in efficient doping of Al-rich AlGaN

Wang,

Xu,

Zhang

et al. 2024

J. Semicond.

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The development of semiconductors is always accompanied by the progress in controllable doping techniques. Taking AlGaN-based ultraviolet (UV) emitters as an example, despite a peak wall-plug efficiency of 15.3% at the wavelength of 275 nm, there is still a huge gap in comparison with GaN-based visible light-emitting diodes (LEDs), mainly attributed to the inefficient doping of AlGaN with increase of the Al composition. First, p-doping of Al-rich AlGaN is a long-standing challenge and the low hole concentration seriously restricts the carrier injection efficiency. Although p-GaN cladding layers are widely adopted as a compromise, the high injection barrier of holes as well as the inevitable loss of light extraction cannot be neglected. While in terms of n-doping the main issue is the degradation of the electrical property when the Al composition exceeds 80%, resulting in a low electrical efficiency in sub-250 nm UV-LEDs. This review summarizes the recent advances and outlines the major challenges in the efficient doping of Al-rich AlGaN, meanwhile the corresponding approaches pursued to overcome the doping issues are discussed in detail.

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Section: Introductionmentioning

confidence: 99%

Progress in efficient doping of Al-rich AlGaN

Wang,

Xu,

Zhang

et al. 2024

J. Semicond.

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“…While controlled defect formation has reached an excellent level of maturity in traditional semiconductors such as Si and GaAs, this is not the case in wide-bandgap semiconductors, where the concentration of deep levels is significant and still strongly impacts the performance of the devices. In fact, deep levels are responsible for several physical phenomena, including carrier trapping, which leads to parametric instability [1][2][3][4][5] and degradation of the dynamic performance [6][7][8][9]; they can act as recombination centers [10,11], thus contributing to a decrease in the internal quantum efficiency of light emitters [12][13][14][15], a decrease in the carrier lifetime [16], and limited spectral purity of optoelectronic devices [17][18][19][20]. In addition, trap states can assist tunneling processes, which have detrimental effects on the reliability of several devices, including high electron mobility transistors (HEMTs) [21][22][23] and light-emitting diodes (LEDs) [24][25][26][27], and promote leakage current [22,28].…”

Section: Introductionmentioning

confidence: 99%

Advanced defect spectroscopy in wide-bandgap semiconductors: review and recent results

Fregolent,

Piva,

Buffolo

et al. 2024

J. Phys. D: Appl. Phys.

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The study of deep level defects in semiconductors has always played a strategic role for the development of electronic and optoelectronic devices. In fact, deep levels have a strong impact on many of the device properties, including the efficiency, stability, and reliability because they can drive several physical process. Despite the advancements in crystal growth, wide and ultrawide bandgap semiconductors (such as gallium nitride and gallium oxide) are still strongly affected by the formation of defects that in general can act as carrier traps or generation-recombination centers. Conventional techniques used for deep level analysis in silicon need to be adapted for identifying and characterizing defects in wide bandap materials. This topical review paper presents an overview of reviews the theory of deep levels in semiconductor; in addition, we present a review and original results and on the application, limits and perspectives of two widely adopted most common deep -levels detection techniques, namely capacitance deep level transient spectroscopy and deep level optical spectroscopy, with specific focus on wide bandgap semiconductors. Finally, the most common traps of GaN and β-Ga2O3 are reviewed.

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Progress and Outlook of 10% Efficient AlGaN‐Based (290–310 nm) Band UVB LEDs

Khan,

Yamada,

Hirayama

2024

Physica Status Solidi (a)

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Eco‐friendly aluminum gallium nitride (AlGaN) materials for the epitaxial growth of ultraviolet‐B (UVB) light emitting diodes (LEDs) on c‐Sapphire have attracted much attention due to their low fabrication cost and possibility of high external‐quantum efficiency (EQE) and light power. However, the long‐term low wall plugs efficiency (WPE) and light power remain a significant bottleneck impeding the commercialization of UVB LED modules. Our special growth techniques for 50% relaxed and 4µm‐thick AlGaN buffer layer (BL) are available to achieve a maximum internal‐quantum efficiency (IQE) surpassing 57% in 300 nm‐Band UVB LEDs. In this review paper, we describe the impact of special growth of thick AlGaN BL as well as n‐AlGaN electron injection layer (EIL) and their crystal quality on the (290‐310nm)‐Band LED’s performances, compared to the conventional n‐AlGaN/p‐GaN based UVB LEDs. The last 6 years have seen large improvements in the AlGaN‐based UVB LED, with efficiencies improved by over 10% at Riken. The main drivers have been improved electrical, optical design, better carriers confinement in the multi‐quantum wells (MQWs) of the UVB LEDs and the generation as well as transportation of hole toward the MQWs. Also, the influence of a thin “Valley” layer in p‐type multi‐quantum barrier electron‐blocking‐layer (p‐MQB EBL) on 2D hole generation and hole injection via intra‐band tunneling (HIT) was attempted. Briefly, these improvements at Riken in the development of high‐efficiency transparent UVB LEDs are including the modulation of Al compositions in the p‐AlGaN hole injection layer (HIL), fabrication methods in MOCVD, and p‐side contact materials including highly reflective p‐electrodes. Notably, we highlight the effects of undoped (ud)‐AlGaN final barrier (FB) of quantum‐well strategies against the electron blocking and promoting the hole tunneling and incorporation of the soft polarized Mg‐doped p‐type AlGaN HIL for better hole injection toward the MQWs to improve the performance of UVB LEDs. As a result, high hole concentration ∽ 2 × 1016 cm−3 in the Al‐graded p‐AlGaN HIL, where the hole‐trap level appeared to have been effectively suppressed by excimer laser annealing (ELA) treatment, and quite low resistivity of 24 Ω‐cm at room temperature (RT) was achieved. Optically, enhanced reflection from Ni/Mg or Ni/Al p‐electrode and improved light extraction within the transparent p‐AlGaN LED have had a large impact. In particular, the transparent AlGaN‐based 290‐310 nm UVB LED has improved significantly in recent years and is now almost approaching that of UVC LED (EQE ∽ 10%). Such new features have increased the efficiencies of transparent 310 nm and 290‐304 nm UVB LEDs, respectively, to a recently confirmed 4.7% and 9.6% with light powers of 29 mW and 40 mW on wafer, world record values of a mere 2 year ago. Finally, we give our perspectives to combine photonic, crystals and electrical constraints into practical architectures for AlGaN‐based UVB LEDs and also identify future research directions as well as potential applications of UVB LED modules technologies, such as those in immunotherapy (psoriasis, vitiligo), vulgaris treatment (310 nm), plant growth under UVB lightning (310 nm), the production of vitamin D3 in the human body (293‐304 nm), the production of phytochemicals in green leaves of vegetables (310 nm) and inactivation of SARS‐CoV‐2.This article is protected by copyright. All rights reserved.

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Temperature-dependent electroluminescence of stressed and unstressed InAlGaN multi-quantum well UVB LEDs

Cited by 6 publications

References 26 publications

Progress in efficient doping of Al-rich AlGaN

Progress in efficient doping of Al-rich AlGaN

Advanced defect spectroscopy in wide-bandgap semiconductors: review and recent results

Progress and Outlook of 10% Efficient AlGaN‐Based (290–310 nm) Band UVB LEDs

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