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Effect of electron blocking layer doping and composition on the performance of 310 nm light emitting diodes
2017, Kolbe, Tim, Knauer, Arne, Rass, Jens, Cho, Hyun Kyong, Hagedorn, Sylvia, Einfeldt, Sven, Kneissl, Michael, Weyers, Markus
The effects of composition and p-doping profile of the AlGaN:Mg electron blocking layer (EBL) in 310 nm ultraviolet B (UV-B) light emitting diodes (LEDs) have been investigated. The carrier injection and internal quantum efficiency of the LEDs were simulated and compared to electroluminescence measurements. The light output power depends strongly on the temporal biscyclopentadienylmagnesium (Cp 2 Mg) carrier gas flow profile during growth as well as on the aluminum profile of the AlGaN:Mg EBL. The highest emission power has been found for an EBL with the highest Cp 2 Mg carrier gas flow and a gradually decreasing aluminum content in direction to the p-side of the LED. This effect is attributed to an improved carrier injection and confinement that prevents electron leakage into the p-doped region of the LED with a simultaneously enhanced carrier injection into the active region.
The 2020 UV emitter roadmap
2020, Amano, Hiroshi, Collazo, Ramón, De Santi, Carlo, Einfeldt, Sven, Funato, Mitsuru, Glaab, Johannes, Hagedorn, Sylvia, Hirano, Akira, Hirayama, Hideki, Ishii, Ryota, Kashima, Yukio, Kawakami, Yoichi, Kirste, Ronny, Kneissl, Michael, Martin, Robert, Mehnke, Frank, Meneghini, Matteo, Ougazzaden, Abdallah, Parbrook, Peter J., Rajan, Siddharth, Reddy, Pramod, Römer, Friedhard, Friedhard, Jan, Sarkar, Biplab, Scholz, Ferdinand, Schowalter, Leo J, Shields, Philip, Sitar, Zlatko, Sulmoni, Luca, Wang, Tao, Wernicke, Tim, Weyers, Markus, Witzigmann, Bernd, Wu, Yuh-Renn, Wunderer, Thomas, Zhang, Yuewei
Solid state UV emitters have many advantages over conventional UV sources. The (Al,In,Ga)N material system is best suited to produce LEDs and laser diodes from 400 nm down to 210 nm - due to its large and tuneable direct band gap, n- and p-doping capability up to the largest bandgap material AlN and a growth and fabrication technology compatible with the current visible InGaN-based LED production. However AlGaN based UV-emitters still suffer from numerous challenges compared to their visible counterparts that become most obvious by consideration of their light output power, operation voltage and long term stability. Most of these challenges are related to the large bandgap of the materials. However, the development since the first realization of UV electroluminescence in the 1970s shows that an improvement in understanding and technology allows the performance of UV emitters to be pushed far beyond the current state. One example is the very recent realization of edge emitting laser diodes emitting in the UVC at 271.8 nm and in the UVB spectral range at 298 nm. This roadmap summarizes the current state of the art for the most important aspects of UV emitters, their challenges and provides an outlook for future developments. © 2020 IOP Publishing Ltd.
Temperature-Dependent Charge Carrier Diffusion in [0001¯] Direction of GaN Determined by Luminescence Evaluation of Buried InGaN Quantum Wells
2020, Netzel, Carsten, Hoffmann, Veit, Tomm, Jens W., Mahler, Felix, Einfeldt, Sven, Weyers, Markus
Temperature-dependent transport of photoexcited charge carriers through a nominally undoped, c-plane GaN layer toward buried InGaN quantum wells is investigated by continuous-wave and time-resolved photoluminescence spectroscopy. The excitation of the buried InGaN quantum wells is dominated by charge carrier diffusion through the GaN layer; photon recycling contributes only slightly. With temperature decreasing from 310 to 10 K, the diffusion length in [0001⎯⎯] direction increases from 250 to 600 nm in the GaN layer. The diffusion length at 300 K also increases from 100 to 300 nm when increasing the excitation power density from 20 to 500 W cm−2. The diffusion constant decreases from the low-temperature value of ∼7 to 1.5 cm2 s−1 at 310 K. The temperature dependence of the diffusion constant indicates that the diffusivity at room temperature is limited by optical phonon scattering. Consequently, higher diffusion constants in GaN-based devices require a reduced operation temperature. To increase diffusion lengths at a fixed temperature, the effective recombination time has to be prolonged by reducing the number of nonradiative recombination centers.
Skin tolerant inactivation of multiresistant pathogens using far-UVC LEDs
2021, Glaab, Johannes, Lobo-Ploch, Neysha, Cho, Hyun Kyong, Filler, Thomas, Gundlach, Heiko, Guttmann, Martin, Hagedorn, Sylvia, Lohan, Silke B., Mehnke, Frank, Schleusener, Johannes, Sicher, Claudia, Sulmoni, Luca, Wernicke, Tim, Wittenbecher, Lucas, Woggon, Ulrike, Zwicker, Paula, Kramer, Axel, Meinke, Martina C., Kneissl, Michael, Weyers, Markus, Winterwerber, Ulrike, Einfeldt, Sven
Multiresistant pathogens such as methicillin-resistant Staphylococcus aureus (MRSA) cause serious postoperative infections. A skin tolerant far-UVC (< 240 nm) irradiation system for their inactivation is presented here. It uses UVC LEDs in combination with a spectral filter and provides a peak wavelength of 233 nm, with a full width at half maximum of 12 nm, and an irradiance of 44 µW/cm2. MRSA bacteria in different concentrations on blood agar plates were inactivated with irradiation doses in the range of 15–40 mJ/cm2. Porcine skin irradiated with a dose of 40 mJ/cm2 at 233 nm showed only 3.7% CPD and 2.3% 6-4PP DNA damage. Corresponding irradiation at 254 nm caused 11–14 times higher damage. Thus, the skin damage caused by the disinfectant doses is so small that it can be expected to be compensated by the skin's natural repair mechanisms. LED-based far-UVC lamps could therefore soon be used in everyday clinical practice to eradicate multiresistant pathogens directly on humans.
Improved Efficiency of Ultraviolet B Light-Emitting Diodes with Optimized p-Side
2020, Kolbe, Tim, Knauer, Arne, Rass, Jens, Cho, Hyun Kyong, Mogilatenko, Anna, Hagedorn, Sylvia, Lobo Ploch, Neysha, Einfeldt, Sven, Weyers, Markus
The effects of design and thicknesses of different optically transparent p-current spreading layers [short-period superlattice, superlattice (SL), and bulk p- (Formula presented.)] as well as the type and thickness of the p-GaN cap layer on the electrical and optical characteristics of 310 nm ultraviolet light-emitting diodes (LEDs) are investigated. Scanning transmission electron microscopy measurements display self-organized composition variations in the nonpseudomorphically grown SLs, reducing the effect of increased hole injection efficiency of a SL. In addition, the effect leads to an increased operation voltage. In contrast, the bulk p-AlGaN layer has a uniform composition and the corresponding LEDs show only a slightly lower output power along with a lower operating voltage. If the thickness of the p-AlGaN bulk layer in the LED is reduced from 150 nm to 50 nm, the output power increases and the operating voltage decreases. Finally, LEDs with a nonuniform (Formula presented.) -GaN cap layer from a 3D island-like growth mode feature the highest output power and operating voltage. In contrast, the output power and operating voltage of LEDs with a smooth and closed cap depend on the thickness of (Formula presented.) -GaN. The highest output power and lowest operating voltage are achieved for LEDs with the thinnest (Formula presented.) -GaN cap. © 2020 The Authors. Published by Wiley-VCH GmbH
Comparison of Ultraviolet B Light‐Emitting Diodes with Single or Triple Quantum Wells
2021, Kolbe, Tim, Knauer, Arne, Ruschel, Jan, Rass, Jens, Kyong Cho, Hyun, Hagedorn, Sylvia, Glaab, Johannes, Lobo Ploch, Neysha, Einfeldt, Sven, Weyers, Markus
Light-emitting diodes (LEDs) with an emission wavelength of 310 nm containing either a single or a triple quantum well are compared regarding their efficiency and long-term stability. In addition, the influence of the thickness of the lower quantum well barrier and the quantum well thickness in single quantum well (SQW) LEDs is investigated. Electroluminescence measurements show a 28% higher initial output power for the SQW LEDs compared with the triple quantum well (TQW) LEDs because of larger spatial overlap of the carriers in the SQW as revealed by electro-optical simulations of the LED heterostructures. However, TQW LEDs show a higher output power than SQW LEDs after 1 h operation under harsh conditions. For SQW LEDs, it is found that for a thicker lower quantum well barrier (65 nm instead of 25 nm) the initial output power decreases by ≈15%. A thicker SQW (3 nm instead of 1.6 nm) reduces the initial output power by even 45% but increases the lifetime by a factor of 6 which is attributed to reduced Auger recombination from an enhanced spatial separation of electrons and holes in the quantum wells due to the quantum-confined Stark effect.