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- Bergmann, Michael Alexander, 1989, et al.
(författare)
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Increased Light Extraction of Thin-Film Flip-Chip UVB LEDs by Surface Texturing
- 2023
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Ingår i: ACS Photonics. - : American Chemical Society (ACS). - 2330-4022. ; 10:2, s. 368-373
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Tidskriftsartikel (refereegranskat)abstract
- Ultraviolet light-emitting diodes (LEDs) suffer from a low wall-plug efficiency, which is to a large extent limited by the poor light extraction efficiency (LEE). A thin-film flip-chip (TFFC) design with a roughened N-polar AlGaN surface can substantially improve this. We here demonstrate an enabling technology to realize TFFC LEDs emitting in the UVB range (280-320 nm), which includes standard LED processing in combination with electrochemical etching to remove the substrate. The integration of the electrochemical etching is achieved by epitaxial sacrificial and etch block layers in combination with encapsulation of the LED. The LEE was enhanced by around 25% when the N-polar AlGaN side of the TFFC LEDs was chemically roughened, reaching an external quantum efficiency of 2.25%. By further optimizing the surface structure, our ray-tracing simulations predict a higher LEE from the TFFC LEDs than flip-chip LEDs and a resulting higher wall-plug efficiency.
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| 2. |
- Bergmann, Michael Alexander, 1989, et al.
(författare)
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Thin-film flip-chip UVB LEDs realized by electrochemical etching
- 2022
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- We will give an overview of different concepts to increase the light extraction efficiency (LEE) of ultraviolet (UV) light-emitting diodes (LEDs) with a focus on thin-film flip-chip (TFFC) devices. Optical simulations show that a TFFC design can greatly improve the LEE with a transparent p-side, reflective contacts, and optimized surface roughening. We will demonstrate UVB-emitting TFFC LEDs based on our fabrication platform for AlGaN thin films with high aluminum content. The fabrication is compatible with a standard LED process and uses substrate removal based on selective electrochemical etching as the key enabling technology.
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| 3. |
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| 4. |
- Cardinali, G., et al.
(författare)
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Low-Threshold AlGaN-based UVB VCSELs enabled by post-growth cavity detuning
- 2022
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 121:10
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Tidskriftsartikel (refereegranskat)abstract
- The performance of vertical-cavity surface-emitting lasers (VCSELs) is strongly dependent on the spectral detuning between the gain peak and the resonance wavelength. Here, we use angle-resolved photoluminescence spectroscopy to investigate the emission properties of AlGaN-based VCSELs emitting in the ultraviolet-B spectral range with different detuning between the photoluminescence peak of the quantum-wells and the resonance wavelength. Accurate setting of the cavity length, and thereby the resonance wavelength, is accomplished by using doping-selective electrochemical etching of AlGaN sacrificial layers for substrate removal combined with deposition of dielectric spacer layers. By matching the resonance wavelength to the quantum-wells photoluminescence peak, a threshold power density of 0.4 MW/cm2 was achieved, and this was possible only for smooth etched surfaces with a root mean square roughness below 2 nm. These results demonstrate the importance of accurate cavity length control and surface smoothness to achieve low-Threshold AlGaN-based ultraviolet VCSELs.
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| 7. |
- Haglund, Åsa, 1976, et al.
(författare)
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Are blue and ultraviolet VCSELs a reality or just a dream?
- 2020
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Blue-emitting vertical-cavity surface-emitting lasers (VCSELs) with high optical output powers and decent threshold current densities have recently been demonstrated, but the power efficiency is still below 10%. We will give an overview of the challenges to realize high-performing devices and summarize state-of-the-art results, including our schemes for optically guided devices that are used in the best blue VCSELs today. In addition, we will present our method to simultaneously achieve high-reflectivity mirrors and good control over the cavity length for ultraviolet VCSELs. This has resulted in, to the best of our knowledge, the shortest VCSEL emission wavelength around 310 nm.
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