High-Efficiency 1-mm$^{2}$ AlGaInP LEDs Sandwiched by ITO Omni-Directional Reflector and Current-Spreading Layer

Hsu, Shun-Cheng; Wuu, Dong−Sing; Lee, Chong−Yi; Su, Juh-Yuh; Horng, Ray Hua

doi:10.1109/lpt.2007.893820

Cited by 32 publications

(23 citation statements)

References 15 publications

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“…Recent results have successfully demonstrated that released, thin‐film LEDs are integrated with flexible, stretchable, and even biodegradable substrates with better biocompatibilities like improved skin conformance and reduced lesion during implantation . Thin‐film, freestanding red and infrared (IR) LEDs based on gallium arsenide can be easily formed by selective sacrificial etching; however, conventional techniques for thin‐film GaN based purple/blue/green LED release and integration typically rely on sophisticated process steps including laser liftoff (LLO) (for GaN on sapphire), chemical etching (for GaN on Si), wafer bonding, layer transfer, device pick and place, etc., thus limiting their use. While GaN LED epitaxial liftoff and integration with flexible substrates have been extensively exploited for various planar device architectures like GaN LEDs on graphene, BN, glasses with nanovoids, Si, SiC‐on‐insulator, the performance of these devices is still inferior to their counterparts on conventional sapphire substrates, in terms of their current–voltage characteristics, quantum efficiencies, etc.…”

mentioning

confidence: 99%

Heterogeneous Integration of Microscale GaN Light‐Emitting Diodes and Their Electrical, Optical, and Thermal Characteristics on Flexible Substrates

Liu

et al. 2017

Adv Materials Technologies

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LEDs that can be utilized as implantable light sources have been playing increasingly important roles in neuroscience research, along with the development of genetically encoded actuators and indicators. [3,4] In particular, gallium nitride (GaN)/indium gallium nitride (InGaN) based blue LEDs are utilized as implantable light sources for optogenetic stimulation and/or exciting fluorophores for neural signal sensing. [5,6] High performance GaN blue LEDs are typically grown on rigid, single crystalline substrates including sapphire, [7,8] silicon (Si) [1] and silicon carbide (SiC), [9] and novel strategies on growing and releasing GaN devices on unusual substrates like zinc dioxide coated graphene, [10] boron nitride (BN), [11] amorphous glasses, [12] nanovoid-mediated substrates, [13] etc. are also actively explored. [14] Although diced bare LED chips have found their uses in wearable and implantable systems by flip-chip bonding, [15,16] thinfilm LEDs (with thicknesses less than 10 µm) with various emission wavelengths that are released from original growth substrates and integrated onto flexible and stretchable substrates are more desirable for biomedical applications. [17] Recent results have successfully demonstrated that released, thinfilm LEDs are integrated with flexible, stretchable, and even biodegradable substrates with better biocompatibilities like improved skin conformance and reduced lesion during implantation. [5,18,19] Thin-film, freestanding red and infrared (IR) LEDs based on gallium arsenide can be easily formed by selective sacrificial etching; [20] however, conventional techniques for thinfilm GaN based purple/blue/green LED release and integration typically rely on sophisticated process steps including laser liftoff (LLO) (for GaN on sapphire), [21,22] chemical etching (for GaN on Si), [1,23,24] wafer bonding, [25][26][27] layer transfer, [11] device pick and place, [28,29] etc., [30,31] thus limiting their use. While GaN LED epitaxial liftoff and integration with flexible substrates have been extensively exploited for various planar device architectures like GaN LEDs on graphene, [7,10] BN, [11] glasses with nanovoids, [12,13] Si, [32] SiC-on-insulator, [9] the performance of these devices is still inferior to their counterparts on conventional sapphire substrates, in terms of their current-voltage characteristics, quantum efficiencies, etc. Therefore, it is highly desirable to develop simple and reliable technologies to implement the mainstream, state-of-the-art GaN LEDs (for example,

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mentioning

confidence: 99%

Heterogeneous Integration of Microscale GaN Light‐Emitting Diodes and Their Electrical, Optical, and Thermal Characteristics on Flexible Substrates

Liu

et al. 2017

Adv Materials Technologies

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“…Since non-uniformity occurs due to the lateral resistance of p-type layer, modification of physical thickness might not be the right solution. Many researches have tried to solve this problem by using spreading layers [17][18][19]. Until now, indium-tin-oxide (ITO) has been used broadly as a current spreading layer for its transparency and low resistance [20][21][22].…”

Section: Introductionmentioning

confidence: 99%

Effects of Current Spreading in GaN-based Light-emitting Diodes Using ITO Spreading Pad

Kim¹,

Kım²,

Park³

et al. 2015

JSTS:Journal of Semiconductor Technology and Science

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Abstract-In conventional LEDs, a mesa-structure is usually used and it causes the current to be overcrowded in a specific region. We propose a novel structure of GaN-based LED to overcome this problem. In order to distribute the current in an active region, a spreading pad is inserted at the p-type region in the GaN based LED device. The inserted spreading pad helps the current flow because it is more conductive than the p-type GaN layer. By performing electrical and optical simulations, the effects of the spreading pad insertion are confirmed. The results of electrical simulation show that the current spreads more uniformly and more radiative recombination is produced as well. Moreover, from the optical simulation, it is revealed that the ITO is less absorptive material than p-GaN if the condition of specific wavelength sources is satisfied. Considering all of the results, we can conclude that the luminescent power is enhanced by the spreading pad.

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“…However, the external efficiency of AlGaInP LED is limited by the light absorption of a GaAs substrate and the narrow critical angle of total internal reflection at the semiconductor-air interface. The output-power efficiency of AlGaInP LED can be improved using a once or twice wafer-transferring technique to reduce the light absorption of GaAs substrate [1] [2]. The external efficiency of AlGaInP LED is mainly limited by difficulty of light extraction.…”

Section: Introductionmentioning

confidence: 99%

Study of Aluminum-doped zinc oxide current spreading layer on P-side up thin-film AlGaInP-based light-emitting diodes by ALD

et al. 2015

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A twice wafer-transfer technique can be used to fabricate high-brightness p-side-up thin-film AlGaInP-based light-emitting diodes (LEDs) with an aluminum-doped zinc oxide (AZO) thin films transparent conductive layer deposited on a GaP window layer. The GaP window layer consist of the two different doping profile, the carbon doped Gap (GaP:C) window layer of 50 nm is on the top of Mg doped GaP window layer of 8 μm. The GaP:C window layer is used to improved the ohmic contact properties of GaP:C/AZO. The AZO with different cycle ratio of Zn:Al (15:1, 20:1 and 25:1) is deposited on GaP:C window layer as current spreading layer by atomic layer deposition. The AZO layer can be used to improve light extraction, which enhances light output power. The output power of p-side-up thin-film AlGaInP LED with an AZO layer of 20:1 cycle ratio has improved up to 19.2 % at injection current of 350 mA, as compared with that of LED without AZO film. The p-side-up thin-film AlGaInP LED with AZO current spreading layer exhibited excellent performance stability, the emission wavelength shift of p-side-up thin-film AlGaInP LED without and with AZO thin film(Zn:Al=20:1) are 17 nm and 3 nm under the injection current increased from 20 mA to 1000mA, respectively. This stability can be attributed to the following factors: 1) Refractive index matching, performed by introducing AZO thin film between the epoxy and the GaP window layer enhances light extraction; and 2) the favorable thermal dissipation of the silicon substrate reduces thermal degradation.

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High-Efficiency 1-mm$^{2}$ AlGaInP LEDs Sandwiched by ITO Omni-Directional Reflector and Current-Spreading Layer

Cited by 32 publications

References 15 publications

Heterogeneous Integration of Microscale GaN Light‐Emitting Diodes and Their Electrical, Optical, and Thermal Characteristics on Flexible Substrates

Heterogeneous Integration of Microscale GaN Light‐Emitting Diodes and Their Electrical, Optical, and Thermal Characteristics on Flexible Substrates

Effects of Current Spreading in GaN-based Light-emitting Diodes Using ITO Spreading Pad

Study of Aluminum-doped zinc oxide current spreading layer on P-side up thin-film AlGaInP-based light-emitting diodes by ALD

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