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Author: Einfeldt, Sven × Author: Knauer, Arne × Author: Weyers, Markus × Has files: Yes × Type: Text ×

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    Effect of electron blocking layer doping and composition on the performance of 310 nm light emitting diodes
    (Basel : MDPI, 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.
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    Improved Efficiency of Ultraviolet B Light-Emitting Diodes with Optimized p-Side
    (Weinheim : Wiley-VCH, 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
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    Comparison of Ultraviolet B Light‐Emitting Diodes with Single or Triple Quantum Wells
    (Weinheim : Wiley-VCH, 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.