Improved output power of GaN-based ultraviolet light-emitting diodes with sputtered AlN nucleation layer

Chiu, C. H.; Lin, Yue; Tsai, Ming-Tsung; Lin, Bangjiang; Li, Z. Y.; Tu, Po-Min; Huang, Shih‐Yu; Hsu, Earl; Uen, Wu‐Yih; Lee, Wei-I; Kuo, Hao‐Chung

doi:10.1016/j.jcrysgro.2014.10.013

Cited by 16 publications

(17 citation statements)

References 31 publications

(29 reference statements)

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“…Furthermore, several techniques, such as epitaxial lateral overgrowth (ELO) 17 18 19 , pendeoepitaxy 20 , cantilever epitaxy 21 , in-situ SiN x nanomasks 22 , and patterned sapphire substrate (PSS) 23 24 25 have been employed to reduce TD density. It is reported that high-quality GaN epilayers with reduced TD density can be obtained using a sputtered AlN NL on sapphire substrate 26 27 28 29 30 . The quality of GaN epilayers is sensitive to the growth of NL.…”

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confidence: 99%

Effects of GaN/AlGaN/Sputtered AlN nucleation layers on performance of GaN-based ultraviolet light-emitting diodes

Zhou

Liu

et al. 2017

Sci Rep

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We report on the demonstration of GaN-based ultraviolet light-emitting diodes (UV LEDs) emitting at 375 nm grown on patterned sapphire substrate (PSS) with in-situ low temperature GaN/AlGaN nucleation layers (NLs) and ex-situ sputtered AlN NL. The threading dislocation (TD) densities in GaN-based UV LEDs with GaN/AlGaN/sputtered AlN NLs were determined by high-resolution X-ray diffraction (XRD) and cross-sectional transmission electron microscopy (TEM), which revealed that the TD density in UV LED with AlGaN NL was the highest, whereas that in UV LED with sputtered AlN NL was the lowest. The light output power (LOP) of UV LED with AlGaN NL was 18.2% higher than that of UV LED with GaN NL owing to a decrease in the absorption of 375 nm UV light in the AlGaN NL with a larger bandgap. Using a sputtered AlN NL instead of the AlGaN NL, the LOP of UV LED was further enhanced by 11.3%, which is attributed to reduced TD density in InGaN/AlInGaN active region. In the sputtered AlN thickness range of 10–25 nm, the LOP of UV LED with 15-nm-thick sputtered AlN NL was the highest, revealing that optimum thickness of the sputtered AlN NL is around 15 nm.

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confidence: 99%

Effects of GaN/AlGaN/Sputtered AlN nucleation layers on performance of GaN-based ultraviolet light-emitting diodes

Zhou

Liu

et al. 2017

Sci Rep

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“…Chiu et al of Hsinchu Chiao Tung University utilized a sputtered AlN nucleation layer grown on a PSS to enhance the quality of their epitaxial layer. The threading dislocation densities (TDDs) were reduced from 6 × 10 7 cm −2 to 2.5 × 10 7 cm −2 at the interface between the u-GaN layers in conventional and AlN PSS devices, respectively [26]. The results are shown in Figure 4.…”

Section: Immature Epitaxial Technology Of Highmentioning

confidence: 92%

Perspectives on UVC LED: Its Progress and Application

et al. 2021

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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.

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“…[22][23][24] For example, Lin et al, 21 investigating the effect of an oxide layer on PSS (OPSS) on the performance of LEDs, reported that the output power of OPSS LEDs was 6.2% higher z E-mail: tyseong@korea.ac.kr than that of conventional LEDs. In addition, Chang et al, 22 investigating the effect of a high-temperature (HT) (1050…”

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confidence: 99%

“…20 Thus, to further improve the crystallinity of GaN layers, the surface characteristics of PSS were modified by using an oxide layer 21 or an AlN nucleation layer. [22][23][24] For example, Lin et al, 21 investigating the effect of an oxide layer on PSS (OPSS) on the performance of LEDs, reported that the output power of OPSS LEDs was 6.2% higher z E-mail: tyseong@korea.ac.kr than that of conventional LEDs. In addition, Chang et al, 22 investigating the effect of a high-temperature (HT) (1050…”

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confidence: 99%

“…The output power (at 20 mA) of the LEDs with the ex situ AlN layer was improved by approximately 5.73% compared to that of the LEDs with the in situ AlN layer. Chiu et al, 24 investigating the effects of in situ MOCVD GaN and ex situ sputtered AlN nucleation layers on the output performance of UV (380 nm)-LEDs grown on PSS, showed that the UV-LEDs grown on the sputtered AlN nucleation layer had better crystalline quality compared to those with the GaN nucleation layer. In other words, the samples with the GaN nucleation layer contained a number of screw and mixed dislocations on the tip and sidewall region of the hemisphere, while fewer screw and mixed dislocations were formed in the sample with the AlN nucleation layer.…”

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confidence: 99%

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Comparison of the Performance of Lateral and Vertical InGaN/GaN-Based Light-Emitting Diodes with GaN and AlN Nucleation Layers

Kang

Choi

Song

et al. 2015

ECS J. Solid State Sci. Technol.

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We investigated the effects of in situ GaN and sputtered AlN nucleation layers on the output power of GaN-based blue (445 nm) LEDs on patterned sapphire substrate (PSS) and planar sapphire substrates. Both the PSS LEDs and planar LEDs showed the same operation voltages, but the LEDs with the AlN layer had much lower reverse leakage current at −15 V. The LEDs with the AlN layer showed higher external quantum efficiency (EQE) at low current regions than those with the GaN nucleation layer. However, the AlN nucleation layer LEDs experienced a little more severe efficiency droop than did the GaN layer LEDs. It was shown that the AlN nucleation layer samples contained fewer defects than the GaN nucleation layer samples. The Raman spectral results showed that the AlN nucleation layer samples experienced higher compressive stress than the GaN nucleation layer samples. Simulation results also showed that both the AlN nucleation layer and air voids in the GaN nucleation layer samples hardly affected the light extraction efficiency. Based on the electrical, X-ray diffraction (XRD), cathodoluminescence (CL), and Raman results, the electrical behavior of the PSS and planar LEDs are described and discussed. InGaN/GaN-based light-emitting diodes (LEDs) are technologically important because of their use in a variety of emitting device applications, which cover wavelengths from green to ultraviolet (UV) spectra.1-4 Currently, high-brightness InGaN/GaN-based LEDs are commercially available. On the one hand, in order to realize general illumination application, the output performance of LEDs should be improved further. One of the major barriers to the enhancement of the light output efficiency of GaN-based LEDs is a high density of threading dislocations (TDs) (in the range of 10 8 -10 10 cm -2 ), 5 which are generated during GaN growth because of the large lattice mismatch and thermal expansion coefficient difference between GaN and sapphire substrate.6,7 Thus, it is crucial to develop ways of reducing TD density to enhance the light output performance. To minimize the generation of TDs, different methods have been proposed, including epitaxial lateral overgrowth (ELOG), [8][9][10][11] SiO 2 patterned mask, 12,13 and ELOG on patterned sapphire substrate (PSS). 14-19 Among them, ELOG on PSS are most commonly used to grow high-quality GaNbased epitaxial layers. For example, Kissinger et al., 15 investigating the output performance of blue LEDs fabricated on lens PSS (LPSS), reported that LPSS-LEDs exhibited 250% higher luminous intensity at an injection current of 20 mA than conventional LEDs and 117% higher emission angle than conventional LEDs. Wuu et al., 18 investigating the effect of hole-PSS on the output performance of near-UV GaN-based LEDs, reported that typical lamp-form PSS-LEDs had an external quantum efficiency of 14.1%, which is higher than that of conventional LEDs. The improvement was attributed to the decrease in TD density and the increase in light extraction efficiency. It is well known that the nucleation layer...

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Improved output power of GaN-based ultraviolet light-emitting diodes with sputtered AlN nucleation layer

Cited by 16 publications

References 31 publications

Effects of GaN/AlGaN/Sputtered AlN nucleation layers on performance of GaN-based ultraviolet light-emitting diodes

Effects of GaN/AlGaN/Sputtered AlN nucleation layers on performance of GaN-based ultraviolet light-emitting diodes

Perspectives on UVC LED: Its Progress and Application

Comparison of the Performance of Lateral and Vertical InGaN/GaN-Based Light-Emitting Diodes with GaN and AlN Nucleation Layers

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