This study presents a novel approach to mitigate electron overflow in deep ultraviolet (UV) AlGaN light-emitting diodes (LEDs) by integrating engineered quantum barriers (QBs) with a concave shape and an optimized AlGaN superlattice (SL) electron blocking layer (EBL). The concave QBs reduce electron leakage by lowering the electron thermal velocity and mean free path, enhancing electron capture in the active region. The SL EBL further reduces electron overflow without compromising hole transport. At a wavelength of ~253.7 nm, the proposed LED demonstrates a 2.67× improvement in internal quantum efficiency (IQE) and a 2.64× increase in output power at 150 mA injection, with electron leakage reduced by ~4 orders of magnitude compared to conventional LEDs. The efficiency droop is found to be just 2.32%.

Although AlGaN-based deep ultraviolet (UV) light-emitting diodes (LEDs) have been studied extensively, their quantum efficiency and optical output power still remain extremely low compared to the InGaN-based visible color LEDs. Electron leakage has been identified as one of the most possible reasons for the low internal quantum efficiency (IQE) in AlGaN based UV LEDs. The integration of a p-doped AlGaN electron blocking layer (EBL) or/and increasing the conduction band barrier heights with prompt utilization of higher Al composition quantum barriers (QBs) in the LED could mitigate the electron leakage problem to an extent, but not completely. In this context, we introduce a promising approach to alleviate the electron overflow without using EBL by utilizing graded concave QBs instead of conventional QBs in AlGaN UV LEDs. Overall, the carrier transportation, confinement capability and radiative recombination are significantly improved. As a result, the IQE, and output power of the proposed concave QB LED were enhanced by ~25.4% and ~25.6% compared to the conventional LED for emission at ~254 nm, under 60 mA injection current.

We report our study on the enhanced light extraction efficiency (LEE) of the 280nm AlInN nanowire ultraviolet light-emitting diodes (LEDs) using different surface passivation approaches and photonic crystal structures. With a ~ 30nm Si3N4 as surface passivation, the AlInN LED could achieve relatively high LEE of ~ 41.5%, while the unpassivated LED has an average LEE of ~ 23.5%. Moreover, the periodically arranged nanowire LED arrays in hexagonal structure exhibit high LEE of 61.4% which is almost two times higher compared to that of the randomly arranged nanowire LEDs. Additionally, the AlInN nanowire ultraviolet LEDs show highly transverse-magnetic polarized emission.

The p-type AlGaN electron barrier layer (EBL) has been widely used to suppress electron leakage from the active region of AlGaN-based deep ultraviolet (UV) light-emitting diodes (LEDs). However, the conventional EBL can reduce the electron leakage partially and invertedly affects the hole injection due to the formation of positive polarization sheet charges at the hetero-interface. Recently, EBL-free LED structures have received significant attention due to the improved carrier transportation and reduced electron leakage. In this context, we present a novel band-engineered EBL-free AlGaN UV LED structure that uses polarization-controlled composition-graded convex quantum barriers (QBs) instead of traditional QBs and analyzed its performance theoretically. Our proposed structure opens a new path to control the electron leakage due to both a gradual increase in the effective conduction band barrier height and mitigated electrostatic field in the active region. As a result, the internal quantum efficiency and output power of the reported EBL-free structure are boosted significantly compared to the traditional AlGaN UV LED at ~260 nm emission wavelength. Experimental demonstration of such a unique LED design can show the way to generate high-power deep UV light sources for practical applications.

The formation of positive sheet polarization charges at the interface of the last quantum barrier (QB) and the conventional p -type electron-blocking layer (EBL) creates significant band bending, leading to severe electron leakage and poor hole injection in III-nitride light-emitting diodes. We report that the positive sheet polarization charges are mitigated by employing a lattice matched AlGaN last QB. Electron leakage is dramatically reduced due to the increased effective conduction band height at the last QB and EBL. Furthermore, it favors hole injection into the active region due to the reduced effective valance band height for EBL.

In this paper, a light-emitting diode in the ultra-violet range (UV-LED) with multiple-quantum wells (MQWs) of InGaN/GaN is designed and analyzed through Technology Computer-Aided Design (TCAD) simulations. The polarization effects in III-nitride heterojunction and the effects of graded composition in the electron blocking layer (EBL) are exploited to enhance the performance of the proposed UV-LED. It is observed that the effect of graded composition in the EBL helps to enhance the electrical and optical performance of the LED, thereby enabling the achievement of some promising results. The simulation-based results demonstrated that superior internal efficiency and an inferior leakage current are achieved by using a graded Al composition in the EBL rather than a uniform composition. The reported results also confirm the remarkable improvement of the light output power by 17% at ∼100 mA when using the graded composition and also show a reduction in series resistance leading to more current. Graded Al composition in the EBL results in the enhancement of electroluminescence spectra (i.e., an increase in the peak of the spectral density).

We report on the demonstration of electron blocking layer free AlInN nanowire light-emitting diodes (LEDs) operating in the 280–365 nm wavelength region. The molecular beam epitaxial grown AlInN nanowires have a relatively high internal quantum efficiency of > 52%. Moreover, we show that the light extraction efficiency of the nanowires could reach ~ 63% for hexagonal photonic crystal nanowire structures which is significantly higher compared to that of the random nanowire arrays. This study provides significant insights into the design and fabrication of a new type of high-performance AlInN nanowire ultraviolet light-emitters.

High efficiency, high color rendition and low-cost light-emitting diodes (LEDs) with low power consumption, long lifetime and high reliability are highly expected for general lighting illumination, smartphones, smartwatches, virtual reality (VR), augmented reality (AR) headsets, and micro-display applications. Nonetheless, the achievement of deep green to red-emitting LEDs using conventional III-nitride quantum well heterostructures has been difficult, due to the presence of large densities of dislocations, strong polarization fields, poor hole transport, and carrier delocalization [1]. The external quantum efficiency (EQE) of the blue and green InGaN LEDs surpassed 80% and 53%, respectively. However, due to the aforementioned issues, the current InGaN red LEDs with high Indium composition exhibit extremely low EQE which is less than 3% [2]. In this regard, LEDs using nanowire structures offer dramatically reduced strain-induced polarization fields and dislocation densities, providing ideal material structure for high efficiency full-color and even white light emission without using phosphor-converters. In this study, we have successfully designed, and fabricated high efficiency red-emitting nanowire heterostructures and demonstrated micro-LEDs with stable and strong emission at ~645 nm. Moreover, the micro-LEDs have high internal quantum efficiency of >40%. The InGaN/AlGaN nanowire micro-LED structures are grown by RF plasma-assisted molecular beam epitaxy (MBE) under nitrogen-rich condition. The LED structure consists of a 250 nm n- GaN nanowire template, 10 couples of 3 nm AlGaN quantum barrier (QB)/ 3 nm InGaN quantum well (QW) served as the active region, and a 200 nm p- GaN. During the epitaxial growth of AlGaN barriers, an AlGaN shell spontaneously forms, enabling a unique InGaN/AlGaN core-shell structure [3]. The emission color of the micro-LEDs can be defined by controlling the ratio of Ga/In flux and the substrate temperature during the MBE growth process. Detailed growth conditions and the device fabrication can be found elsewhere [3-5]. The nanowires are uniformly arranged on Si substrates, as illustrated in Figure 1(a). Figure 1(b) shows the schematic structure of the fabricated micro-LEDs. Strong red emissions were measured from the InGaN/AlGaN core-shell LEDs, as shown in Figure 1(c). At injection current of 400mA, the peak emission wavelength is at ~645nm. The red-emitting micro-LEDs exhibit stable emissions with a blue-shift of only ~ 4nm under injection current from 50 mA to 400 mA, attributed to the significantly reduced quantum-confined Stark effect (QCSE) in the nanowire structures. Moreover, full color micro-LEDs with device size from 10x10 µm 2 to 100x100 µm 2 have been fabricated using similar approach. Such high efficiency, high color rendering properties, and low power consumption micro-LEDs are promising candidates for emerging AR/VR devices and micro-LED display applications. References: 1. Kim, M.H., et al., Applied Physics Letters, 91 (2007) 183507; 2. Liu, X., et al., Photonics Research, 10 (2022) 587; 3. Philip, M.R., et al., Journal of Vacuum Science & Technology B, 35 (2017)02B108; 4. Bui, H.Q.T., et al., Micromachines, 10 (2019) 492; 5. Jain, B., et al., Optics Express, 28 (2020) 665. Figure 1

Electron leakage is one of the critical challenges in AlGaN ultraviolet (UV) light-emitting diodes (LEDs). In this regard, a p-type AlGaN electron-blocking layer (EBL) has been utilized to suppress electron leakage. However, it affects the hole injection due to the generation of positive polarization sheet charges at the hetero-interface of the EBL and the last quantum barrier (QB). To address this problem, we propose an EBL-free AlGaN UV LED using polarization-engineered graded QBs instead of conventional QBs. The proposed structure could enhance the carrier confinement in the active region and significantly reduces electron leakage due to the progressively increased effective conduction band barrier heights. Substantially, the proposed structure exhibits higher optical power and wall-plug efficiency at 60 mA current injection, which are boosted by ~85.9% and ~53.6% compared to the conventional structure. Such a unique LED design could pave the way for the next generation of high-power deep UV light sources.

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.

In this study, we report highly stable phosphor-free InGaN/AlGaN spontaneously formed core-shell nanowire red micro-light emitting diodes (μLEDs) with 30 × 30 μm2 mesa area directly grown on Si (111) substrates using molecular beam epitaxy.

Though AlGaN ultraviolet (UV) light-emitting diodes (LEDs) have been explored widely, their performance is still limited in the UV B and C regions due to several challenges. Electron leakage is one of the prominent reasons behind the poor performance of AlGaN deep UV LEDs. This problem can be mitigated by integrating the electron-blocking layer (EBL) between the active region and p-region to an extent, not entirely due to the own disadvantages of the EBL. In this regard, we report the achievement of high-performance EBL free AlGaN LEDs using a strip-in-a-barrier structure operating in the UV B and C regions, particularly at 254 nm and 292 nm wavelengths, respectively. Here, we have engineered each quantum barrier by integrating a 1 nm optimized intrinsic AlGaN strip layer in the middle of the QB. The resulting structure could significantly reduce the electron overflow and enhance the output power by ~1.87 times and ~1.48 times for 254 nm and 292 nm LEDs, respectively, compared to the conventional structure. Moreover, internal quantum efficiency droop is reduced notably in the proposed structure at 254 nm and 292 nm wavelengths.

In this work, we have designed an UV-LED with multiple-quantum well of GaN/AlGaN to witness the effect of spontaneous polarization on its output characteristics and it shows some promising results. Using Silvaco TCAD it is observed that the influence of spontaneous polarization helps in improving the optical performance of the device. The built-in electric field induced by spontaneous polarization is considered at hetero-interfaces of GaN LED, which has a significant influence for its output power behavior. The simulation results suggest that the optical power in presence of spontaneous polarization is significantly greater than that compared to conventional LED; it is carried out at a temperature of 300 K. The output current, charge concentration, and the normalized power spectral densities for both the cases are discussed in this paper.

To prevent electron leakage in deep ultraviolet (UV) AlGaN light-emitting diodes (LEDs), Al-rich p-type AlxGa(1−x)N electron blocking layer (EBL) has been utilized. However, the conventional EBL can mitigate the electron overflow only up to some extent and adversely, holes are depleted in the EBL due to the formation of positive sheet polarization charges at the heterointerface of the last quantum barrier (QB)/EBL. Subsequently, the hole injection efficiency of the LED is severely limited. In this regard, we propose an EBL-free AlGaN deep UV LED structure using graded staircase quantum barriers (GSQBs) instead of conventional QBs without affecting the hole injection efficiency. The reported structure exhibits significantly reduced thermal velocity and mean free path of electrons in the active region, thus greatly confines the electrons over there and tremendously decreases the electron leakage into the p-region. Moreover, such specially designed QBs reduce the quantum-confined Stark effect in the active region, thereby improves the electron and hole wavefunctions overlap. As a result, both the internal quantum efficiency and output power of the GSQB structure are ~2.13 times higher than the conventional structure at 60 mA. Importantly, our proposed structure exhibits only ~20.68% efficiency droop during 0–60 mA injection current, which is significantly lower compared to the regular structure.

In this paper, a novel beta-Ga2O3 high electron mobility transistor (BGO-HEMT) with record-high intrinsic unity current gain cut-off frequency (f(T)) of 166 GHz and RF output power (P-OUT) of 2.91 W/mm is demonstrated through 2D device simulations using an appropriate negative differential mobility model. The highly scaled proposed device uses 10 nm AlN barrier layer on 50 nm beta-Ga2O3 buffer with gate-length (L-G) of 50 nm and aspect-ratio (gate length to barrier thickness) of 5 ensures significant gain in high-frequency performance. The novel device design offers very low access and dynamic resistance due to highly doped n(+)access regions, and a finite gap between ohmic contacts and barrier layer to mitigate source choking effect. The device's superior DC and RF performance is well supported by large two-dimensional electron gas (2DEG) density(n(s))of the order of 10(13) cm(-2) due to large band discontinuity in AlN/beta-Ga2O3 heterostructure and highly polarized AlN material. The device shows maximum drain current density (I-DMAX) of similar to 11.5 A/mm and peak transconductance (g(m)) of 0.917 S/mm atV(DS)= 15 V andV(GS)= 0 and - 7 V respectively. Furthermore, the term 2 pi (f(T) x L-G) for the device shows a value of 0.5 x 10(7) cm/s, very close to v(sat) of 1.5 x 10(7) cm/s in beta-Ga2O3. These promising results enhance the potential of beta-Ga(2)O(3)for future high power RF and microwave applications.

We report on the achievement of a new type of ultraviolet light-emitting diodes (LEDs) using AlInN nanowire heterostructures. The molecular beam epitaxial grown AlInN nanowires have relatively high internal quantum efficiency of > 52% at 295nm. The peak emission wavelength is in the range of 280 - 355nm. Moreover, we show that the light extraction efficiency of AlInN nanowire LEDs could reach ~ 63% for hexagonal photonic crystal nanowire structures which is significantly higher compared to the random nanowire arrays. This study provides significant insights into the design and fabrication of new type of high performance AlInN nanowire ultraviolet light-emitters.

Ultraviolet‐B (UVB) AlGaN light‐emitting diodes (LEDs) with a hybrid hole injection layer comprising a 5 nm thin p‐Al x Ga (1− x ) N linearly graded layer (LGL), x from 0.65 to 0.50, and a 15 nm conventional p‐AlGaN layer are proposed for ≈284 nm wavelength emission. The introduced p‐Al x Ga (1− x ) N LGL effectively improves the confinement of the electrons in the active region by effectively increasing the conduction band barrier height. Moreover, it enhances the hole injection capability into the active region by energizing the holes that minimize the effective valence band barrier height. As a result, the proposed LED structure exhibits an incredibly reduced electron leakage, ten times lower than that of the conventional structure. Moreover, the output power and electroluminescence intensity of the proposed structure are enhanced by approximately twice at 60 mA current injection. Thus, the LGL LED structure can be a potential candidate for high‐power UV light emitters.

One of the probable reasons behind the limitation of light extraction efficiency (LEE) in III-nitride nanowire (NW) deep ultraviolet (UV) light-emitting diodes (LEDs) is the presence of the high surface density states that significantly contribute to the non-radiative recombination near the surface. Herein, we investigate the LEE of a single AlInN NW UV LED in the entire UV wavelength regime using finite-difference time-domain simulations. It is found that these LEDs favor transverse-magnetic (TM) polarized LEE over transverse-electric (TE) polarized emission. Further, we examine the role of the HfO2 surface passivation layer in the improvement of LEE of AlInN NW LED at ~282 nm wavelength. Our results show that the TM-polarized LEE of such LED without any passivation is only ~25.2%, whereas the maximum recorded LEE is ~40.6% with the utilization of 40 nm HfO2 passivation layer. This study provides a promising approach for enhancing the LEE of NW UV LEDs.

In this paper, a light emitting diode in the ultra-violet range (UV-LED) with quantum well of AlInGaN is designed and analyzed through technology computer-aided design (TCAD) simulations. A thorough study is performed to find out the output optical characteristics of the LED. During the experiment we have varied the thickness of the well and aluminum concentration in the electron blocking layer in order to realize its impact on the device performance. The structure of the device and the characteristics of epitaxial layers play a very noteworthy role in the device’s performance. The yield characteristics of the device depend on its structural layer. Because of this, various properties are optimized in order to improve the device’s final performance. The LED device has gained importance over the past few decades. These are available for almost all ranges of wavelength right from deep ultra-violet to infra-red light region. The most efficient UV-LEDs are fabricated using AlInGaN with different atom proportions. The emission wavelength is correlated with the band gap of materials for such optoelectronic devices which can be varied from UV to IR.