Nanowire Light-emitting Diodes Research Articles

Strategically Developed Strong Red‐Emitting Oxyfluoride Nanophosphors for Next‐Generation Lighting Applications

AbstractRed‐emitting nanophosphors have a multirole in improvising the next‐generation bulk/micro/nano‐level lighting devices, particularly in refining white light quality and device performance. Nonetheless, it is difficult to synthesize nanosized phosphors with good yield and paralleled high absorption efficiency both in UV and blue regions, which is critical for modern lighting. Herein, new Mg14Ge4.99+σO24‐x+δFx: Mn4+ red nanoparticles with sizes below 100 nm are designed to improve not only the luminescence but also the blue light absorption. This approach has validated the applicability of red‐emitting nanophosphors into flexible UV and blue nitride nanowire light‐emitting‐diodes (LEDs), and commercial bulk LEDs, for the first time, with boosted intensity and color superiority for a variety of lighting utilizations. For these phosphor LEDs (pc‐LEDs), optimized red nanophosphor with an external quantum efficiency of ≈44.5%, color purity of ≈100%, and thermal stability of ≈72% at 150 °C is used. The optimized nanophosphor is combined with a flexible UV‐AlGaN/GaN nanowire LED and a blue‐InGaN/GaN‐LED. The resultant devices show promising red electroluminescence without any degradation at elevated currents. Finally, several unfamiliar LED packaging is designed with yellow and red phosphors implemented on 2 sets of double LED units to reach CRI > 85. The re‐premeditated LED packages are useful for high‐definition lighting.

Optimization of the Al Composition of the p‐AlGaN Electron Blocking Layer in GaInN/GaN Multiquantum‐Shell Nanowire LEDs

The aim is to develop highly efficient GaInN/GaN nanowire (NW)‐based light‐emitting diodes (LEDs), which are composed of GaN NWs and multiquantum shell (MQS) active regions. These regions incorporate the polar c‐plane, nonpolar r‐plane, and semipolar m‐plane. A challenge with MQS‐LEDs is that the current path through the c‐plane MQS tends to dominate under low‐current injection conditions. Given that the MQS on the c‐plane is very defective, this injection current is mainly subjected to nonradiative recombination. Therefore, this study explores various optimizations of the p‐AlGaN electron blocking layers (EBLs) to minimize the current injection into the MQS in the c‐plane region. The samples are subsequently grown using a specific process. This involves n‐GaN NWs, GaInN/GaN‐based quantum shells, p‐AlGaN EBLs with different Al compositions, and p‐GaN shells. All these are developed by metal–organic vapor phase epitaxy on an n‐GaN template featuring a SiO2 hole pattern. NW LEDs are fabricated and subsequently their device characteristics are investigated. Under low‐current injection, the sample with a lower Al composition exhibits higher luminescence intensity. However, this trend reverses when the injection current increases. The findings suggest that AI composition and thickness in the p‐AlGaN EBL significantly affect the output power and the emission wavelength.

화합물 반도체 기반의 유연 발광소자 및 디스플레이 제작

This article presents a review of research activities over past decades focused on the fabrication of flexible light-emitting diodes (LEDs) and micro-LED displays. LEDs exhibit excellent material characteristics, including high radiative recombination rates, high carrier mobility, and ultra-long-term stability. These features make LEDs promising candidates for not only the future metaverse display but flexible display applications. However, the brittleness of compound semiconductor thin films poses challenges for creating deformable LED devices. Consequently, significant efforts have been dedicated to imparting deformability to LED devices and displays. We initially discuss a display prepared using a nanowire-assembly process, followed by a strategy involving thin film LEDs for flexible device fabrication. Vertical nanowire LED arrays are presented, along with a discussion of their advantages for flexible devices and displays. Furthermore, we review the selective-area epitaxy of vertical nanowire LED arrays. Finally, we briefly introduce the assembly methods of LEDs onto backplane circuits, addressing several important issues, including the misalignment of LED transfers onto backplane circuits. We conclude with personal remarks on the challenges and future perspectives for research on flexible micro-LED displays.

Optimized method of thermoelectric cooler-based thermal management for improving the luminous efficacy of light-emitting diodes

We experimentally performed a method of active cooling for white LED that can reduce the temperature of the LED by using TEC for reducing the temperature of the LED board. The relation of LED board and input power for TEC was investigated to find out the optimized curve of LED board temperature and input power for TEC. Also, the TEC based cooling system was applied for RGBW LEDs. The obtained result is meaningful in LED thermal management, improving the lighting quality and increases the lifespan for both middle and high-power LED types. Full Text: PDF References E.F. Schubert, J.K. Kim, "Solid-State Light Sources Getting Smart", Science, 308, 1274 ¬(2005). CrossRef Q.K. Nguyen, "Emission spectrum modeling of white LEDs light source with using Gaussian function", Photonics Lett. Pol.,15(4), 54 (2023). CrossRef C.C. Sun, S.H. Ma, Q.K. Nguyen, "Advanced LED Solid-State Lighting Optics", Crystals, 10, 758 (2020). CrossRef S.P. Ying, H.K. Fu, W.F. Tang, R.C. Hong, "The Study of Thermal Resistance Deviation of High-Power LEDs", IEEE Trans. Electron Devices, 61, 2843 (2014). CrossRef K. Górecki, P. Ptak, "Compact Modelling of Electrical, Optical and Thermal Properties of Multi-Colour Power LEDs Operating on a Common PCB", Energies, 14, 1286 (2021). CrossRef C.C. Sun, Q.K. Nguyen, T.X. Lee, S.K. Lin, C.S. Wu, T.H. Yang, Y.W.Yu. "Active thermal-fuse for stopping blue light leakage of white light-emitting diodes driven by constant current", Sci. Rep. 12, 12433 (2022). CrossRef Q.K. Nguyen, B. Glorieux, G. Sebe , T.H. Yang, Y.W. Yu , C.C. Sun, "Passive anti-leakage of blue light for phosphor-converted white LEDs with crystal nanocellulose materials", Sci Rep. 13, 13039 (2023). CrossRef N. Bădălan (Drăghici), P. Svasta, C. Marghescu, "A Method for Improving an Active Cooling Solution for LEDs ", IEEE 24th International Symposium for Design and Technology in Electronic Packaging (SIITME), Iași, Romania (2018). CrossRef A. Fan, R. Bonner, S. Sharratt, Y.S. Ju, "An innovative passive cooling method for high performance light-emitting diodes", 28th Annual IEEE Semiconductor Thermal Measurement and Management Symposium (SEMI-THERM), 319-324 (2012). CrossRef D.W. Kim, E. Rahim, A. Bar-Cohen, B. Han, "Direct Submount Cooling of High-Power LEDs", Compon. Packag. Technol., 33, 698 (2010). CrossRef N. Guan, N. Amador-Mendez, A. Kunti, A. Babichev, S. Das, A. Kapoor, N. Gogneau, J. Eymery, F.H. Julien, C. Durand, M. Tchernycheva, "Heat Dissipation in Flexible Nitride Nanowire Light-Emitting Diodes", Nanomater, 10, 2271 (2020). CrossRef S. Li, J.L. Liu, L. Ding, J.X. Liu, J. Xu, Y. Peng, M.X. Chen, "Active Thermal Management of High-Power LED Through Chip on Thermoelectric Cooler", IEEE Trans. Electron Devices, 68, 1753 (2021). CrossRef G.R. Sui, J.J. Chen, H. Ni, Y.Y. Ma, X.M. Gao, N. Wang, "Improvement of LED Performance With an Integrated Thermoelectric Cooling Package", IEEE Access, 8, 116535 (2020). CrossRef

Characterization of nanowire light-emitting diodes with InP/InAsP heterostructures emitting in telecom band

We report the growth and characterization of InP/InAsP/InP nanowires (NWs) and NW LEDs (NW-LEDs), which emit light at telecom wavelengths. InP-based NWs were grown by selective-area metal-organic vapor-phase epitaxy, and a thin InAsP layer was embedded in the NWs. The NW exhibited emission lines in their low-temperature photoluminescence spectra, suggesting the formation of quantum dots (QDs) in the NW. NW-LED operation was demonstrated at both room and low temperatures in the telecom band, but it was found that the emission wavelength range and blueshift behavior induced by current injection differed considerably between room and low temperatures. Our results suggest that an efficient path for carrier injection into the active InAsP layer should be explored for NW-QD-based single-photon sources operating via current-injection.

High-performance red-emitting InGaN/AlGaN nanowire light-emitting diodes grown through porous template

High-performance red-emitting InGaN/AlGaN nanowire light-emitting diodes grown through porous template

Formation and Optical Characteristics of GaN:Eu/GaN Nanowires for Applications in Light-Emitting Diodes

This paper reviews our recent research about the formation and optical characteristics of GaN:Eu/GaN nanowires (NWs) by metalorganic vapor phase epitaxy for application in GaN-based red light-emitting diodes (LEDs). Two types of GaN:Eu/GaN NWs with different configurations are introduced, core–shell and axial geometries. The configuration of GaN:Eu layers on GaN core NWs can be controlled by changing the growth conditions, and affects the properties of Eu luminescence in the GaN NWs. Next, the optimization of the p-GaN growth conditions is performed to allow to form the p-GaN shell layers on the NWs with the pedestal of the NWs free from radial overgrowth, resulting in efficient electrical isolation between top and bottom part of the NWs. Then, the fabrication process of the NW LEDs towards future possible realization of flexible devices is established, including an etch-back process of the PDMS membranes to expose the top p-GaN contact layers. Finally, a proto-type of p-GaN/GaN:Eu/n-GaN NW LEDs on sapphire substrates is fabricated to characterize the device properties. Sharp red luminescence at room temperature from Eu3+ ions is observed under current injection. These results would pave the way towards the realization of flexible light-emitting devices utilizing NW structures based on compound semiconductors.

High‐efficiency nanowire light‐emitting diodes for augmented reality and virtual reality displays

AbstractThrough 3D dipole cloud model, RGB (red, green, and blue) nanowire light‐emitting diode (LED) structures are geometrically optimized to exhibit a narrower radiation pattern, weaker angular color shift, and higher optical efficiency. In comparison with micro‐LEDs whose external quantum efficiency is dependent on the mesa size, these RGB nanowire LEDs are more efficient than micro‐LEDs when the chip size is below 20, 80, and 10 μm, respectively. As a result, nanowire LED is a promising candidate for augmented reality and virtual reality displays where high‐resolution density and efficient directional light emission are desired.

Effect of substrate rotation speed on AlGaN nanowire deep ultraviolet light-emitting diodes by molecular beam epitaxy

Aluminum gallium nitride (AlGaN) nanowires by molecular beam epitaxy (MBE) have become an emerging platform for semiconductor deep ultraviolet (UV) light-emitting diodes (LEDs). Despite of the progress, much less attention has been paid to the effect of substrate rotation speed on the device performance. Herein, we investigate the effect of the substrate rotation speed on the nanowire height and diameter uniformity, as well as the electrical and optical performance of MBE-grown AlGaN nanowire deep UV LED structures with low and high substrate rotation speeds. It is found that by increasing the substrate rotation speed from 4 revolutions per minute (rpm) to 15 rpm, the statistical variation of the nanowire height and diameter is reduced significantly. Increasing the substrate rotation speed also improves the device electrical performance, with a factor of 4 reduction on the device series resistance. This improved electrical performance further transfers to the improved optical performance. The underlying mechanisms for these improvements are also discussed.

A red-emitting micrometer scale LED with external quantum efficiency >8%

Significant efforts are being put into the development of efficient micrometer-scale light emitting diodes (LEDs) for future display technologies due to their marked benefits over existing displays. To date, however, the efficiency of microLED devices remains significantly lower than that of conventional broad-area devices. The deterioration in device performance with smaller device size has been linked to the plasma damage induced on mesa sidewalls during device fabrication. Here, we studied bottom-up red-emitting nanowire LEDs with different Mg doping levels in the p-GaN layer. The resulting sub-micron LED devices show a distinct improvement in efficiency with increasing Mg dopant incorporation. Through optimization of the doping, we measured an external quantum efficiency of ∼8.3% and a wall-plug efficiency of ∼4.6%, at a current density of ∼1 A/cm2, for a red-emitting sub-micrometer scale LED operating at >630 nm. This study highlights the importance of p-doping in microLEDs for attaining high efficiency performance in nanostructure-based devices.

Optically and electrically invariant multi-color single InGaN/GaN nanowire light-emitting diodes on a silicon substrate under mechanical compression.

Recent years have seen immense advances in electroluminescent InGaN-based light-emitting diodes (LEDs) that may revolutionize lighting and display technologies. Driven by the need for the development of submicrometer-sized, multicolor light sources monolithically integrated on a single chip, it is necessary to accurately characterize the size-dependent electroluminescence (EL) properties of selective-area grown single InGaN-based nanowire (NW) LEDs. Moreover, InGaN-based planar LEDs generally undergo; external mechanical compression induced by the packaging process which could potentially degrade the emission efficiency this further motivates us to investigate the size-dependent EL properties of single InGaN-based NW LEDs on a Si substrate under external mechanical compression. In this work, we perform opto-electro-mechanical characterization of single InGaN/GaN NWs using a scanning electron microscopy (SEM)-based multi-physical characterization technique. We first tested the size-dependent EL properties of selective-area grown single InGaN/GaN NWs on a Si substrate with a high injection current density up to 12.99 kA cm-2. In addition, the effect of external mechanical compression on the EL properties of the single NWs was investigated. Stable EL properties (no degradation of EL peak intensity and no peak wavelength shift) and electrical characteristics have been observed by applying a 5 μN compressive force to single NWs with different diameters. The results confirm no degradation of the NW light output with the applied stress (up to 62.2 MPa) and demonstrate the superior optical and electrical robustness of single InGaN/GaN NW LEDs under mechanical compression.

Current injection and luminescence properties of wurtzite InP nanowires with crystal phase transition

We characterized the current injection and electroluminescence (EL) properties of wurtzite (WZ) InP nanowire (NW) light-emitting diodes (LEDs) with axial junctions. The EL spectra of two samples with the same LED junction structure exhibited two different behaviors. One showed a single EL peak originating from the zinc-blende (ZB)-InP bandgap. The other showed two EL peaks originating from the ZB and WZ phases. This difference in EL behavior is attributed to the difference in the contact position and to depletion layer spreading. Clarification of the origin of the different EL peaks is important for optimizing the NW-LED structure.

Inverse Tapered AlGaN Micropillar and Nanowire LEDs for Improved Light Extraction Efficiency at 270 nm

Deep-ultraviolet (DUV) light emitting diodes (LEDs) show great potential in a wide range of applications, but suffer from poor external quantum efficiencies (EQEs) when compared to visible LEDs, due to their exceptionally poor light extraction efficiency (η <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">EXT</sub> ). One successful method of improving the η <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">EXT</sub> of DUV LEDs is the use of micropillar and nanowire arrays. Our previous works have reported the development of an “inverse taper” profile in AlGaN micropillars during wet etching in heated hydroxyl-based chemistries. Here, we study the effects of inverse tapering on the η <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">EXT</sub> of AlGaN microstructures and nanostructures at 270 nm using finite-difference time-domain simulations, in accordance with our experimental results. Results show that η <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">EXT</sub> can be increased from ∼45% to more than 95% for TM-polarized emission in microstructures with diameters of 1 μm and heights >1 μm, and from ∼35% to more than 85% for TE-polarized emission by an inverse taper angle of 5 °. Results for nanostructures also indicate significant η <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">EXT</sub> improvements through tuning of the inverse taper angle. These findings, along with our demonstration of inverse tapered high Al-content AlGaN micro and nanostructures, could enable the development of record-high EQE DUV LEDs based on arrays of high aspect ratio structures with high η <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">EXT</sub> .

(Invited) Enhanced Efficiency of AlInN Nanowire Ultraviolet Light-Emitting Diodes Using Photonic Crystal Structures

High efficiency ultraviolet (UV) light-emitting diodes (LEDs) are in high demand for a wide range of applications [1-3]. Due to its wide bandgap, covering from deep UV to near visible, AlGaN semiconductor has been intensively studied for high efficiency UV LEDs. However, the performance of AlGaN UV LEDs is still limited, especially in the deep UV wavelength region, due to large dislocation density and extremely inefficient p-type doping in AlGaN film. Therefore, AlGaN UV LEDs have been suffering from low internal quantum efficiency (IQE), poor light extraction efficiency (LEE), and low external quantum efficiency (EQE). Alternatively, AlInN alloy is relatively unexplored for light-emitters even though it holds great potential application in UV and visible light-emitting devices. Recent studies have reported that InAlN has a large optical gain for deep UV LEDs. In this context, we have successfully developed AlInN nanowire LEDs with strong emission in the UV wavelength regime. The AlInN nanowires achieved a high IQE of >50% and significantly strong Transverse Magnetic (TM) polarized emission at 299nm.The AlInN nanowire LED structures were spontaneously grown on n-Si (111) substrates under nitrogen rich conditions by a Veeco GEN II molecular beam epitaxy (MBE) system. The AlInN nanowire was grown on GaN nanowire template. The device active region consists of ~ 100 nm n-Al0.78In0.22N, 40 nm undoped Al0.75In0.25N well and 100 nm p-Al0.78In0.22N layers. The GaN nanowire segments were grown at ~ 800 °C, nitrogen flow rate of 0.5-1.0 sccm, and forward plasma power of ~ 400 W. However, the growth temperature of the active region was at ~ 670 ̶ 700 °C to increase the In incorporation in AlInN segments and the nitrogen flow rate was kept at 2.5 sccm. The MBE grown AlInN under nitrogen rich condition offers an effective approach to eliminate the composition inhomogeneity in the AlInN. The nanowires are vertically aligned to the Si substrate with quite uniform dimension, as illustrated in Figure 1(a). Figure 1(b) presents the structure of a single AlInN nanowire LED. The photoluminescence (PL) spectra of AlInN nanowires were measured using a 266 nm diode-pumped solid-state laser as the excitation source. The peak emissions vary from 280nm to 365nm by varying the Al/In composition in the AlInN layers. The peak emission is shifted to shorter wavelength when the substrate temperature gets increase which is attributed to the increased In adatom desorption at higher growth temperature, resulted in the reduced In composition in the AlInN segment. The AlInN/GaN nanowire exhibits relatively high IQE which is estimated of ~ 52% at room temperature [3, 4]. Illustrated in Figure 1(c), the UV nanowire LED holds strong emission spectra at ~299 nm with a negligible shift in the peak wavelength, attributing to the high crystalline quality and reduced quantum-confined Stark effect in the AlInN nanowires. The LED has a low turn-on voltage of ~5V and low reverse leakage current less, i.e., ~0.5 µA at -8.6V. Moreover, as shown in Figure 1(d), we have demonstrated that the LEE of the AlInN nanowire LEDs could reach ~ 63% using hexagonal photonic crystal nanowire structures which is significantly higher compared to that of the random nanowire arrays [5]. This study paves the way for the development of high-power ultraviolet light-emitters using AlInN nanowire arrays.

(Invited) Enhanced Efficiency of AlInN Nanowire Ultraviolet Light-Emitting Diodes Using Photonic Crystal Structures

In this paper, we report on the enhanced light extraction efficiency (LEE) of AlInN nanowire ultraviolet light-emitting diodes (LEDs) at an emission wavelength of 283 nm using the surface passivation approach and hexagonal photonic crystal structures. Several dielectric materials including SiO2, Si3N4, HfO2, AlN, and BN, have been investigated as the surface passivation layer for the AlInN nanowire LEDs. The LEDs using these dielectric materials show significantly improved LEE compared to that of the unpassivated ultraviolet nanowire LEDs. With a 35nm Si3N4 as surface passivation, the AlInN LED could achieve a LEE of ~ 42.6%, while the unpassivated LED could only have an average LEE of ~ 25.2%. Moreover, the LEE of the AlInN nanowire LEDs could be further increased using hexagonal photonic crystal structures. The periodically arranged nanowire LED arrays could reach up to 63.4% which is almost two times higher compared to that of the random nanowire LEDs. Additionally, the AlInN nanowire ultraviolet LEDs exhibit highly transverse-magnetic polarized emission.

AlGaN nanowire deep ultraviolet LEDs with polarization enhanced tunnel junction and p-AlGaN layer by molecular beam epitaxy

In this work, we report the growth, fabrication, and characterization of aluminum gallium nitride (AlGaN) nanowire deep ultraviolet light-emitting diodes with a polarization engineered tunnel junction (TJ) and p-AlGaN layer. The major takeaway from this study is: first, devices emitting at around 250 nm with a maximum external quantum efficiency of around 0.01% are demonstrated. Second, the effect of the electric polarization field in the n+-Al0.1Ga0.9N/GaN/p+-Al0.1Ga0.9N TJ due to the incorporation of the GaN layer is observed by comparing the current-voltage (I–V) characteristics of devices with different GaN thicknesses. The incorporation of the GaN layer improves the I–V characteristics due to the improved tunneling process originating from the band bending induced by the polarization charges at GaN and AlGaN heterointerfaces. Third, the role of the graded p-AlGaN layer on the device's electrical performance is also elucidated. It is found that the graded p-AlGaN layer plays a significant role in improving the device electrical performance. Finally, the improved device electrical performance also transfers to the device optical performance.

High-Resolution Mapping of Strain Partitioning and Relaxation in InGaN/GaN Nanowire Heterostructures.

Growing an In x Ga1− x N/GaN (InGaN/GaN) multi‐quantum well (MQW) heterostructure in nanowire (NW) form is expected to overcome limitations inherent in light‐emitting diodes (LEDs) based on the conventional planar heterostructure. The epitaxial strain induced in InGaN/GaN MQW heterostructure can be relaxed through the sidewalls of NW, which is beneficial to LEDs because a much larger misfit strain with higher indium concentration can be accommodated with reduced piezoelectric polarization fields. The strain relaxation, however, renders highly complex strain distribution within the NW heterostructure. Here the authors show that complementary strain mapping using scanning transmission electron microscopy and dark‐field inline holography can comprehend the strain distribution within the axial In0.3Ga0.7N/GaN MQW heterostructure embedded in GaN NW by providing the strain maps which can cover the entire NW and fine details near the sidewalls. With the quantitative evaluation by 3D finite element modelling, it is confirmed that the observed complex strain distribution is induced by the strain relaxation leading to the strain partitioning between InGaN quantum disk, GaN quantum well, and the surrounding epitaxial GaN shell. The authors further show that the strain maps provide the strain tensor components which are crucial for accurate assessment of the strain‐induced piezoelectric fields in NW LEDs.

(Invited) Recent Progress on Molecular Beam Epitaxy of AlGaN Nanowires for Deep Ultraviolet Light Emitting Devices

Aluminum gallium nitride (AlGaN) nanowires become an attractive material platform for semiconductor deep ultraviolet (UV) light emitting devices. In this paper, recent progress on AlGaN nanowire deep UV light-emitting diodes (LEDs) is presented. We first show that by exploiting the compositional fluctuations within the AlGaN nanowires, light emission wavelength as short as 209 nm can be obtained. Angle dependence studies further indicate a dominant surface emission, originated from the light scattering effect of nanowires. We further demonstrate that graphene electrode can be a current spreading layer for AlGaN nanowire deep UV LEDs and compared with using thin metal contact the light output power is improved. We lastly describe a new direction of employing nanowires for AlGaN deep UV LEDs.

InP nanowire light-emitting diodes with different pn-junction structures

We report on the characterization of wurtzite (WZ) InP nanowire (NW) light-emitting diodes (LEDs) with different pn junctions (axial and radial). The series resistance tended to be smaller in the NW-LED using core–shell InP NWs with a radial pn junction than in the NW-LED using InP NWs with an axial pn junction, indicating that radial pn junctions are more suitable for current injection. The electroluminescence (EL) properties of both NW LEDs revealed that the EL had three peaks originating from the zinc-blende (ZB) phase, WZ phase, and ZB/WZ heterojunction. Transmission electron microscopy showed that the dominant EL in the radial pn junction originated from the ZB/WZ interface across the stacking faults.

AlGaN nanowire deep ultraviolet light emitting diodes with graphene electrode

Despite graphene being an attractive transparent conductive electrode for semiconductor deep ultraviolet (UV) light emitting diodes (LEDs), there have been no experimental demonstrations of any kind of semiconductor deep UV LEDs using a graphene electrode. Moreover, although aluminum gallium nitride (AlGaN) alloys in the format of nanowires are an appealing platform for surface-emitting vertical semiconductor deep UV LEDs, in particular, at short wavelengths, there are few demonstrations of AlGaN nanowire UV LEDs with a graphene electrode. In this work, we show that transferred graphene can serve as the top electrode for AlGaN nanowire deep UV LEDs, and devices emitting down to around 240 nm are demonstrated. Compared to using metal, graphene improves both the light output power and external quantum efficiency. Nonetheless, devices with a graphene electrode show a more severe efficiency droop compared to devices with metal. Here, we attribute the heating effect associated with the large contact resistance to be the major reason for the severe efficiency droop in the devices with a graphene electrode. Detailed scanning electron microscopy and Raman scattering experiments suggest that the nanowire height nonuniformity is the main cause for the large contact resistance; this issue could be potentially alleviated by using nanowires grown by selective area epitaxy that is able to produce nanowires with uniform height. This work, therefore, not only demonstrates the shortest wavelength LEDs using a graphene electrode but also provides a viable path for surface-emitting vertical semiconductor deep UV LEDs at short wavelengths.