Conventional Electron Blocking Layer Research Articles

Low parasitic carrier reservoir of AlGaN-based DUV-LED via controlled-polarization step-graded superlattice electron blocking layer for high luminescence lighting

Achieving high luminescence intensity of deep-ultraviolet light-emitting diode (DUV-LED) is generally performed through the implementation of electron blocking layer (EBL) on the chip’s epilayers. However, the issue of parasitic carrier reservoir that originated from the uncontrolled piezoelectric field polarization has restricted the performance of DUV-LED by reducing the radiative recombination in the active region. This work reports on the numerical computation analysis of the DUV-LED with different types of EBL designs which are reference EBL, conventional superlattice EBL and step-graded superlattice EBL. The analysis of the DUV-LED focuses on the band diagram, carrier concentration at the EBL interfaces, current density of the carrier in the active region, radiative recombination rates, and luminescence spectrum. Remarkably, it is found that the DUV-LED step-graded superlattice EBL provides the polarization-controlled band diagram and emits 272 nm UVC-wavelength in which it is superior in performance compared to the other structures, specifically in terms of its radiated intensity. The parasitic electron and hole reservoir have been reduced by 30% and 60%, respectively. The luminescence intensity was also enhanced by 11% compared with the reference EBL and the IQE obtained by the DUV-LED with step-graded superlattice EBL is 50.12%.

Developing Deep Ultraviolet Laser Diode: Design and Improvement of Al0.62Ga0.38N/Al0.68Ga0.32N Quantum Wells on AlN Substrates for 266 nm DUV Emission

A deep ultraviolet (DUV) laser diode is a compact and efficient semiconductor device that emits laser light in the deep ultraviolet range. Its unique properties make it suitable for a wide range of applications in fields such as manufacturing, research, and healthcare. In this research we propose two Al-graded Electron Blocking Layer (EBL) and quantum barriers (QBs) to improve the performance of AlGaN-based Deep UV-LDs. The electrical properties and optical properties of three structures containing conventional EBL, composition graded increased EBL, and liner graded increased of EBL and QBs were numerically investigated. It was found that the structure-C with linear graded increased EBL and QBs significantly improved the Optical Confinement Factor (OCF) 21%, gain 1600 cm-1, emission power 0.060 W, raised the carrier concentration in the MQWs region, enhanced the stimulated recombination rate and reduced the carrier leakage, of the laser diode (LDs). But at a 100-mA injection current, the threshold current and voltage were reduced to 43 mA and 5.00 V, valance barrier height 270 meV respectively. In compare to the conventional structure, introducing a graded design for both EBL and Quantum Barriers (QBs) with increased aluminum content significantly enhanced the performance of the laser diode (LD). This improvement is essential for advancing Deep Ultraviolet Laser Diodes (DUV-LD) technology.

Optimization of AlGaN-based deep ultraviolet light emitting diodes with superlattice step doped electron blocking layers.

The superlattice electron blocking layer (EBL) has been proposed to reduce the electron leakage of the deep ultraviolet light emitting diodes (DUV-LEDs). However, the hole transport is hindered by the barriers of EBL and the improvement of hole injection efficiency still suffers enormous challenges. The superlattice step doped (SLSD) EBL is proposed to improve the hole injection efficiency while enhancing the electron confinement capability. The SLSD EBL enhances the electron confinement capability by multi-reflection effects on the electron wave function. And a built-in electric field towards the active region is generated by superlattice step doping, which facilitates the transport of holes into the multiple quantum wells. The Advaced Physical Model of Semiconductor Devices (APSYS) software is used to simulate the DUV-LEDs with conventional EBL, superlattice EBL, superlattice doped EBL, and SLSD EBL. The results indicate that the SLSD EBL contributes to the increased electron concentration in the multiple quantum wells, the reduced electron leakage in the p-type region, the increased hole injection current, and the increased radiative recombination rate. When the current is 60 mA, the external quantum efficiency of DUV-LED with SLSD EBL is increased to 5.27% and the output power is increased to 13.81 mW. The SLSD EBL provides a valuable reference for solving the problems of serious electron leakage and insufficient hole injection of the DUV-LEDs.

Optimization of AlGaN-based deep UV LED performance by p-AlInGaN/AlInGaN graded superlattice electron blocking layer.

In this paper, we significantly improved the internal quantum efficiency and output power of AlGaN-based deep UV (DUV) LEDs by replacing the conventional p-AlGaN electron blocking layer (EBL) with the p-AlInGaN/AlInGaN graded superlattice (SL) EBL. Simulation results show that the introduction of the p-AlInGaN graded SL EBL improved the carrier distribution while having the lower electric field, thus increasing the radiative recombination rate in multiple quantum wells (MQWs). The highest IQE obtained by p-AlInGaN/AlInGaN graded SL EBL is 96.6%, which is 44.9% higher than the conventional p-AlGaN EBL with no efficiency droop. At the same time, the output power is 4.6 times that of the conventional p-AlGaN EBL. It is believed that the proposed p-AlInGaN graded SL EBL will be helpful in the development of high-performance DUV LEDs.

Performance Improvement of AlGaN‐Based Deep‐Ultraviolet Light‐Emitting Diodes with Multigradient Electron Blocking Layer and Triangular Last Quantum Barrier

The performance improvements of AlGaN‐based deep ultraviolet light‐emitting diodes (DUV‐LEDs) with multigradient electron blocking layer (EBL) and triangular last quantum barrier (LQB) are investigated. The results show that the maximum internal quantum efficiency (IQE) is improved by 44.9% and light output power (LOP) is improved by 58.1% at 200 A cm−2, exhibiting a tremendous improvement compared to the conventional structure. These improvements are mainly attributed to the fact that both multigradient EBL and triangular LQB can generate negative polarization charges in the graded composition layer, which leads to a significant increase in hole concentration compared to the conventional EBL and LQB structures. Meanwhile, the multigradient EBL can transform the conventional triangular barrier into an arc‐shaped barrier, increasing the electron potential barrier height and decreasing the hole potential barrier height. This unique design suppresses electron leakage and enhances hole injection, leading to a significant enhancement of the IQE and alleviation of the efficiency droop.

Simulation and theoretical study of AlGaN-based deep-ultraviolet light-emitting diodes with a stepped electron barrier layer

Owing to the COVID-19 outbreak, sterilization of deep-ultraviolet light-emitting diodes (DUV LEDs) has attracted increasing attention. Effectively improving the radiative recombination efficiency and mitigating the efficiency degradation, mainly caused by electron leakage and nonradiative recombination, have also emerged as two of the main issues to be addressed. In this study, a DUV LED epitaxial structure with a novel electron-blocking layer (EBL) is proposed. The DUV LED with a luminescence wavelength of ∼297 nm was formed by the stepwise variation of the Al component. Through the simulation and analysis of its performance parameters, we found that, compared to the conventional EBL structure, this new EBL structure not only reduces the electron leakage to the p-region effectively but also increases the hole injection into the active region, resulting in an increase in carrier concentration in the active region, a two-to-three-fold increase in the radiative recombination rate, and a 58% increase in the internal quantum efficiency, thus alleviating the efficiency droop and achieving a more efficient operation at high current densities.

P-AlInN electron blocking layer for AlGaN-based deep-ultraviolet light-emitting diode

Commonly, the Al-rich AlGaN layer acts as electron blocking layer (EBL) to block the overflow of electrons from the active region in conventional AlGaN deep-ultraviolet (DUV) light-emitting diode (LED). However, the Al-rich AlGaN layer leads to the disadvantages of severe electron overflow and hole blocking effect. Herein, we proposed a new AlInN-based EBL to improve the optoelectronic characteristics of AlGaN-based DUV LED. The calculated results show that conventional (fixed Al composition) AlInN EBL has superior hole injection, reduced electron overflow, and lower electric field as compared to conventional AlGaN EBL. By using AlInN EBL, internal quantum efficiency (IQE) drop is reduced by 20%, and light output power improved by 165.30%. It was noticed that conventional AlInN EBL has a 28% IQE drop which can further be minimized by employing AlInN/AlInN superlattice EBL structure. It is found that superlattice EBL improved carrier distribution and reduced electric field resulting in a higher electron-hole wave-function overlap of 55% within multiple quantum wells (MQW) which elevate radiative recombination rate. AlInN superlattice EBL LED has drop-free 93% IQE, twice light output power, and spontaneous emission rate compared to conventional AlInN EBL LED.

Exploring superlattice DBR effect on a micro-LED as an electron blocking layer.

The role of a superlattice distributed Bragg reflector (SL DBR) as the p-type electron blocking layer (EBL) in a GaN micro-light-emitting diode (micro-LED) is numerically investigated to improve wall-plug efficiency (WPE). The DBR consists of AlGaN/GaN superlattice (high refractive index layer) and GaN (low refractive index layer). It is observed that the reflectivity of the p-region and light extraction efficiency (LEE) increase with the number of DBR pairs. The AlGaN/GaN superlattice EBL is well known to reduce the polarization effect and to promote hole injection. Thus, the superlattice DBR structure shows a balanced carrier injection and results in a higher internal quantum efficiency (IQE). In addition, due to the high refractive-index layer replaced by the superlattice, the conductive DBR results in a lower operation voltage. As a result, WPE is improved by 22.9% compared to the identical device with the incorporation of a conventional p-type EBL.

Reduction of efficiency droop by inserting superlattice quaternary-ternary electron blocking layer in GaN-based light-emitting diodes

We report a reduced the unwanted hole blocking of the electron blocking layer (EBL) by replacing the conventional EBL with a quaternary-ternary superlattice electron blocking layer. The effective barrier height for holes is reduced from ~ 348 meV to ~ 261 meV, thus, improving the concentration of holes by ~ 50% with respect to LED with conventional EBL. Similarly, the radiative recombination rate is also improved by ~ 79%. As a result, the overall droop ratio of internal quantum efficiency (IQE) of the proposed LED is reduced to ~ 23% at 100 A/cm2 in comparison to conventional LED.

Improved Performance of Electron Blocking Layer Free AlGaN Deep Ultraviolet Light-Emitting Diodes Using Graded Staircase Barriers.

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.

Improved Performance of GaN-Based Ultraviolet LEDs With Electron Blocking Layers Composed of Double-Peak p-Type Al x Ga1−x N/GaN Superlattice Layers

Past studies have demonstrated the positive impact of step-graded $p$ -type Al x Ga1− x N/GaN superlattice (SL) electron blocking layer (EBL) structures on the efficiency performance of ultraviolet (UV) GaN-based light-emitting diodes (LEDs). However, the optimal Al-grading structure of these SL EBLs remains unclear owing to a lack of systematic investigation. The present work addresses this issue by applying EBL composed of alternating half-peak, single-peak, and double-peak $p$ -type Al x Ga1− x N/GaN SL structures with varying values of $x$ ranging from 0.05 to 0.15 in 0.05 step increments. Simulation analysis is employed to obtain the internal quantum efficiency (IQE), energy band diagrams, polarization compensation factor, hole concentration, and electron concentration of GaN-based UV LEDs with three different SL-EBL structures. The results obtained at an injection current of 200 mA demonstrate that UV LEDs with double-peak SL-EBL structures provide the maximum IQE, which is ~38% greater than that of devices employing the conventional EBL in simulation experiment. This SL-EBL is demonstrated to improve the hole injection and electron overflow performance of GaN-based UV LEDs owing to the polarization charge and lattice mismatch at the p- Al x Ga1− x N/GaN interfaces. The reduced Al composition on the p- GaN side reduces the potential barrier of hole injection. Moreover, the predicted increase in the IQE of GaN-based UV LEDs with the optimal SL-EBL is verified experimentally.

Enhanced hole transport in AlGaN deep ultraviolet light-emitting diodes using a double-sided step graded superlattice electron blocking layer

In this paper, deep ultraviolet AlGaN light-emitting diodes (LEDs) with a novel double-sided step graded superlattice (DSGS) electron blocking layer (EBL) instead of a conventional EBL have been proposed for ∼ 254 n m wavelength emission. The enhanced carrier transport in the DSGS structure results in reduced electron leakage into the p -region, improved hole activation and hole injection, and enhanced output power and external quantum efficiency. The calculations show that output power of the DSGS structure is ∼ 3.56 times higher and electron leakage is ∼ 12 times lower, compared to the conventional structure. Moreover, the efficiency droop at 60 mA in the DSGS LED was found to be ∼ 9.1 % , which is ∼ 4.5 times lower than the regular LED structure.

Double-side step-graded AlGaN electron blocking layer for nearly droop-free GaN-based blue LEDs

Double-side step-graded AlGaN electron blocking layer (EBL) for InGaN/GaN based LEDs with emission wavelength at 415 nm is proposed to develop nearly droop-free performance. The performance comparison of LEDs with double-side step-graded EBL and with conventional EBL reveals that the proposed structure yields 31.50% improved IQE, three-fold higher output power with a very low efficiency droop ∼ (5%) at the current density of 200 A/cm 2 . Such noticeable improvement is justified by critically analyzing and comparing both of the structures in terms of band structure, carrier concentration, electrostatic field and radiative recombination rate. Analysis confirms that double-side step-graded EBL results in superior electron confinement, increased hole injection and higher radiative recombination rate for LEDs. • For the first time Blue-LED with extraordinary droop control has been explored and reported. • Slight variation in the parameters like radiative recombination and electrostatic field have been critically analysed. • Analysis and confirmation of double-side step-graded EBL which results in superior electron confinement. • Effect of double-side step-graded EBL in increasing injection and radiative recombination rate has been reported.

Improved performance of N-face AlGaN-based deep ultraviolet light-emitting diodes with superlattice electron blocking layer

The performance of N-face AlGaN-based deep ultraviolet light-emitting diodes (UV LEDs) with superlattice electron blocking layer (EBL) is investigated by using two-dimensional numerical simulation. The simulated results demonstrate that the adoption of N-face UV LED with superlattice EBL is critical to improve the device’s performance. In comparison with the Ga-face UV LEDs with superlattice and conventional EBL, the N-face device structure with superlattice EBL possesses numerous advantages. By detailedly analyzing the profiles of energy band diagrams, distribution of carrier concentration, and radiative recombination rate, the advantages of N-face UV LED with superlattice EBL are attributed to the higher barrier for electron leakage, and simultaneously reduced barrier for hole injection compared with conventional Ga-face UV LEDs.

Efficiency improvements in AlGaN-based deep ultraviolet light-emitting diodes using inverted-V-shaped graded Al composition electron blocking layer

This paper principally presents the numerical investigation of electron blocking layers (EBL) structures with different Al concentration gradient changing in AlGaN-based deep ultraviolet light emitting diodes (DUV-LEDs). Compared to conventional EBL structure with constant Al composition, the LED with inverted-V-shaped EBL structure has higher output power and carriers recombination rate, but the efficiency droop will decrease obviously while the electron leakage current can reduce much as well. Therefore, the result indicates that appropriate Al component in LED can enhance electron and hole recombination rate in the active region. The improved performance is mainly attribute the sufficient electron-barrier height and relatively higher hole injection efficiency which results from the mitigated band-bending.

Advantages of AlGaN-based deep ultraviolet light-emitting diodes with a superlattice electron blocking layer

The properties of 298nm AlGaN based deep ultraviolet light-emitting diodes (UV LEDs) with different Al mole compositions in the conventional electron blocking layer (EBL) are discussed in this paper, the optimal Al mole composition of the conventional EBL is identified at 0.8. The improved structure with an AlGaN/AlGaN superlattice (SL) electron blocking layer (EBL) was then investigated numerically. The electrical and optical properties, band diagrams, carrier concentrations, radiative recombination rates and internal quantum efficiency (IQE) were investigated by APSYS software, and results show that the deep UV LED with superlattice EBL performed much better than the conventional EBL deep UV LED, attributed to reduced electrons leakage and increased holes injection.

The improvement of deep-ultraviolet light-emitting diodes with gradually decreasing Al content in AlGaN electron blocking layers

Deep-ultraviolet light-emitting diodes (DUV-LEDs) with conventional and specifically designed electron blocking layers (EBLs) are numerical investigated with APSYS simulation program. The results show that the internal quantum efficiency (IQE) and light output power are significantly improved by using a AlGaN EBL with gradually decreasing Al content compared to the conventional EBL with constant Al content and the EBL with gradually increasing Al content. These improvement are mainly attributed to the lower polarization field in EBL and active region as well as the alleviation of band bending in the EBL/p-GaN interface, which lead to less electron leakage and better hole injection efficiency, thus enhance the radiative recombination rate.

Advantages of deep-UV AlGaN light-emitting diodes with an AlGaN/AlGaN superlattices electron blocking layer

In this work, the AlGaN/AlGaN superlattices (SLs) electron blocking layer (EBL) is designed to replace conventional AlGaN EBL in the AlGaN-based deep-UV light-emitting diodes (DUV-LEDs). The simulation results show that the DUV-LEDs with SLs possess higher emission power and internal quantum efficiency as compared to those with conventional EBL, which is attributed to the suppression of electron leakage and the enhancement of hole injection efficiency due to the alleviated strain force and the appropriately modified energy band caused by SLs EBL. The results also demonstrate that the efficiency droop is markedly reduced when the SLs EBL is adopted.

Enhancing Carrier Injection Using Graded Superlattice Electron Blocking Layer for UVB Light-Emitting Diodes

We have studied enhanced carrier injection by having an electron blocking layer ( EBL ) based on a graded superlattice ( SL ) design. Here, we examine, using a self-consistent 6 $\times$ 6 k $\cdot$ p method, the energy band alignment diagrams under equilibrium and forward bias conditions while also considering carrier distribution and recombination rates ( Shockley–Read–Hall, Auger , and radiative recombination rates). The graded SL is based on $\hbox{Al}_{x}\hbox{Ga}_{1-x}\hbox{N}$ (larger bandgap) $\hbox{Al}_{0.5}\hbox{Ga}_{0.5}\hbox{N}$ (smaller bandgap) SL , where $x$ is changed from 0.8 to 0.56 in steps of 0.06. Graded SL was found to be effective in reducing electron leakage and enhancing hole injection into the active region. Due to our band engineering scheme for EBL , four orders-of-magnitude enhancement were observed in the direct recombination rate, as compared with the conventional bulk EBL consisting of $\hbox{Al}_{0.8}\hbox{Ga}_{0.2}\hbox{N}$ . An increase in the spatial overlap of carrier wavefunction was obtained due to polarization-induced band bending in the active region. An efficient single quantum-well ultraviolet-B light-emitting diode was designed, which emits at 280 nm. This is the effective wavelength for water disinfection application, among others.

Tailoring of polarization in electron blocking layer for electron confinement and hole injection in ultraviolet light-emitting diodes

The influence of the AlGaN electron blocking layer (EBL) with graded aluminum composition on electron confinement and hole injection in AlGaN-based ultraviolet light-emitting diodes (LEDs) are investigated. The light output power of LED with graded AlGaN EBL was markedly improved, comparing to LED with conventional EBL. In experimental results, a high increment of 86.7% can be obtained in light output power. Simulation analysis shows that via proper modification of the barrier profile from the last barrier of the active region to EBL, not only the elimination of electron overflow to p-type layer can be achieved but also the hole injection into the active region can be enhanced, compared to a conventional LED structure. The dominant factor to the performance improvement is shown to be the modulation of polarization field by the graded Al composition in EBL.