Enhanced Light Output of UVA GaN Vertical LEDs With Novel DBR Mirrors

Kuo, Shou‐Yi; Hong, Kuo‐Bin; Lu, Tien‐Chang

doi:10.1109/jqe.2015.2502901

Cited by 12 publications

(7 citation statements)

References 24 publications

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“…19 reported the narrow-band distributed Bragg reflectors realized by GaN:Ge modulation-doped structure. The embedded distributed Bragg reflector 20, 21 , the high reflective tin-doped indium oxide/Ag nano-dots/Al-based reflectors 22 , the Ti 3 O 5 /Al 2 O 3 DBR 23 , and the ITO/dielectric DBR 24 were demonstrated to enhance the light extraction process in the UV-LED structures. Furthermore, nanoporous GaN materials with low effective refractive index have been proposed for the DBR structure applications 25–27 .…”

Section: Introductionmentioning

confidence: 99%

Ultraviolet GaN Light-Emitting Diodes with Porous-AlGaN Reflectors

Fan

Syu

et al. 2017

Sci Rep

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A GaN/AlGaN ultraviolet light emitting diode (UV-LED) structure with a porous AlGaN reflector structure has been demonstrated. Inside the UV-LED, the n+-AlGaN/undoped-AlGaN stack structure was transformed into a porous-AlGaN/undoped-AlGaN stack structure through a doping-selective electrochemical etching process. The reflectivity of the porous AlGaN reflector was 93% at 374 nm with a stop-bandwidth of 35 nm. In an angle-dependent reflectance measurement, the central wavelength of the porous AlGaN reflector had blueshift phenomenon by increasing light-incident angle from 10° to 50°. A cut-off wavelength was observed at 349 nm due to the material absorption of the porous-AlGaN/u-AlGaN stack structure. In the treated UV-LED structure, the photoluminescence emission wavelength was measured at 362 nm with a 106° divergent angle covered by the porous-AlGaN reflector. The light output power of the treated UV-LED structure was higher than that of the non-treated UV-LED structure due to the high light reflectance on the embedded porous AlGaN reflector.

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Section: Introductionmentioning

confidence: 99%

Ultraviolet GaN Light-Emitting Diodes with Porous-AlGaN Reflectors

Fan

Syu

et al. 2017

Sci Rep

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“…34,35 However, Kuo et al reported that narrow p-contact holes in thick DBR would result in poor metal sidewall coverage and the non-flat surface for metal bonding. 36 To enable conformal metal coverage across the sidewall of DBR, five pairs of TiO 2 /SiO 2 DBR with total thickness of 621 nm in combination with ITO was used as highly reflective ohmic contact. For reflectance comparison, Ni/Ag (200 nm) with various thicknesses of Ni, namely, 0.5, 1, and 4 nm, and ITO (60 nm)/DBR (621 nm) were deposited on the double side polished sapphire wafer.…”

Section: Resultsmentioning

confidence: 99%

Comparative Study of Highly Reflective ITO/DBR and Ni/Ag ohmic Contacts for GaN-Based Flip-Chip Light-Emitting Diodes

Liu

et al. 2018

ECS J. Solid State Sci. Technol.

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Heat removal and current spreading uniformity are important for the realization of highly efficient light-emitting diodes (LEDs).Here we have compared two types of GaN-based flip-chip LEDs (FCLEDs) with highly reflective indium-tin oxide (ITO)/distributed Bragg reflector (DBR) and Ni/Ag p-type ohmic contacts. The via-based n-type contact structure was implemented to increase the utilization ratio of active region area and improve current spreading over the entire LEDs. Compared with FCLED with Ni/Ag, the FCLED with ITO/DBR shows a 6.3% higher light output power (LOP) at low current density of 31 A/cm 2 (90 mA) due to higher reflectance of ITO/DBR ohmic contact. However, at high injection currents, the Ni/Ag ohmic contact in FCLED alleviates self-heating issue by means of its superior heat dissipation performance. We also found that the less area coverage between ITO and metallization layer have a negative influence on heat dissipation performance of FCLED with ITO/DBR. As a result, the maximum light output power (LOP) of the FCLED with Ni/Ag obtained at 292.8 A/cm 2 is 1.3 times larger than that of FCLED with ITO/DBR obtained at 196.3 A/cm 2 .

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“…The main challenge of developing high-efficiency UV LED chip is to realize the reflective electrode with high reflectivity, good contact and stable operation in 365 nm band. There have been numerous reports on various types of ultraviolet mirrors, including metal mirrors, distributed Bragg reflectors (DBRs), omnidirectional reflectors (ODRs), and tin-doped indium oxide (ITO)/Al reflectors (Lobo et al, 2010;Lin et al, 2010;Takehara et al, 2012;Choi et al, 2013;Nakashima et al, 2013;Chong and Lau, 2014;Kim et al, 2014;Kuo et al, 2015). However, the UV Mirrors reported in the literature still had the problems of low reflectivity in 365 nm band, poor electrical performance in contact with p-AlGaN and bad heat dissipation performance.…”

Section: Introductionmentioning

confidence: 99%

Design and Performance of Ultraviolet 368-nm AlGaN-Based Flip-Chip High-Voltage LEDs with Epitaxial Indium Tin Oxide/Al Reflective Mirror and Symmetry Electrode Arrangement

Wang

Lao

et al. 2022

Front. Mater.

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In this letter, we describe the design and fabrication of high-power AlGaN-based ultraviolet (UV) flip-chip high-voltage light-emitting diodes (LEDs) operating at 368 nm with an epitaxial indium tin oxide (ITO)/Al reflecting mirror and symmetry electrode layout. Metal-organic chemical vapor deposition (MOCVD) was used to grow an ITO thin film as a transparent electrode on the LED surface. At 365 nm, epitaxial ITO thin films exhibited a transmittance of up to 93.6%. Additionally, the epitaxial ITO/Al reflective mirror has a reflectance of 81.2% at 365-nm. To investigate the electrical characteristics, four types of HV-LED micro-cells were constructed with varying n-type mesa structures and p-type interconnect electrodes. We demonstrated a forward voltage (Vf) of 7.86 V at 350 mA with a 2 × 2 mico-cells high-voltage ultraviolet 368-nm flip-chip LED after optimising electrode structure and device process.

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Enhanced Light Output of UVA GaN Vertical LEDs With Novel DBR Mirrors

Cited by 12 publications

References 24 publications

Ultraviolet GaN Light-Emitting Diodes with Porous-AlGaN Reflectors

Ultraviolet GaN Light-Emitting Diodes with Porous-AlGaN Reflectors

Comparative Study of Highly Reflective ITO/DBR and Ni/Ag ohmic Contacts for GaN-Based Flip-Chip Light-Emitting Diodes

Design and Performance of Ultraviolet 368-nm AlGaN-Based Flip-Chip High-Voltage LEDs with Epitaxial Indium Tin Oxide/Al Reflective Mirror and Symmetry Electrode Arrangement

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