Conventional AlGaN Electron Blocking Layer Research Articles

Performance enhancement with thin p-AlInN electron-blocking layer in ultraviolet light-emitting diodes

III-nitride ultraviolet light-emitting diodes (UV LEDs) face low carrier confinement and poor p-doping. In this study, we propose a thin AlInN electron-blocking layer (EBL) in UV LEDs instead of conventional AlGaN EBL. Numerical results demonstrate that UV LED with thin AlInN enhances the optoelectronic performance. The results also reveal that AlGaN EBL is more sensitive to p-doping as compared to AlInN EBL. Thin AlInN layer facilitates hole transportation through intra-band tunneling. Moreover, AlInN has a high conduction band offset that suppresses the electron leakage effectively. Hence, the carrier radiative recombination rate considerably enhances with thin AlInN EBL. The efficiency droop in the proposed LED is also alleviated.

Optimized carrier confinement in deep-ultraviolet light-emitting diodes with AlInGaN/AlInN superlattice electron blocking layer

The optoelectronic characteristics of AlGaN-based deep ultraviolet light-emitting diodes (DUV LEDs) with AlInGaN/AlInN superlattices electron blocking layer (EBL) are numerically investigated. The results show that DUV LED with AlInGaN/AlInN EBL has superior carrier confinement capability over the DUV LED with conventional AlGaN EBL. Hence, the internal quantum efficiency (IQE) and radiative recombination rate of the proposed LED is increased by 49% and 219%, respectively as compared to conventional LED. This is assigned to the optimal recombination of electron-hole pairs in the active zone of the proposed LED. Interestingly, the proposed LED also exhibits near-droop-free efficiency.

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.

The marvelous optical performance of AlGaN-based deep ultraviolet light-emitting diodes with AlInGaN-based last quantum barrier and step electron blocking layer.

The optoelectronic characteristics of AlGaN-based deep ultraviolet light-emitting diodes (DUV LEDs) with quaternary last quantum barrier (QLQB) and step-graded electron blocking layer (EBL) are investigated numerically. The results show that the internal quantum efficiency (IQE) and radiative recombination rate are remarkably improved with AlInGaN step-graded EBL and QLQB as compared to conventional or ternary AlGaN EBL and last quantum barrier (LQB). This significant improvement is assigned to the optimal recombination of electron–hole pairs in the multiple quantum wells (MQWs). It is due to the decrease in strain and lattice mismatch between the epi-layers which alleviates the effective potential barrier height of the conduction band and suppressed the electron leakage without affecting the holes transportation to the active region. Moreover, to figure out quantitatively, the electron and hole quantity increased by ~ 25% and ~ 15%, respectively. Additionally, the IQE and radiative recombination rate are enhanced by 48% and 55%, respectively, as compared to conventional LED. So, we believe that our proposed structure is not only a feasible approach for achieving highly efficient DUV LEDs, but the device physics presented in this study establishes a fruitful understanding of III nitride-based optoelectronic devices.

BAlN for III-nitride UV light-emitting diodes: undoped electron blocking layer

The undoped BAlN electron-blocking layer (EBL) is investigated to replace the conventional AlGaN EBL in light-emitting diodes (LEDs). Numerical studies of the impact of variously doped EBLs on the output characteristics of LEDs demonstrate that the LED performance shows heavy dependence on the p-doping level in the case of the AlGaN EBL, while it shows less dependence on the p-doping level for the BAlN EBL. As a result, we propose an undoped BAlN EBL for LEDs to avoid the p-doping issues, which a major technical challenge in the AlGaN EBL. Without doping, the proposed BAlN EBL structure still possesses a superior capacity in blocking electrons and improving hole injection compared with the AlGaN EBL having high doping. Compared with the Al0.3Ga0.7N EBL with a doping concentration of 1 × 1020 cm−3, the undoped BAlN EBL LED still shows lower droop (only 5%), compatible internal quantum efficiency (2% enhancement), and optical output power (6% enhancement). This study provides a feasible route to addressing electron leakage and insufficient hole injection issues when designing ultraviolet LED structures.

High-performance electron-blocking-layer-free deep ultraviolet light-emitting diodes implementing a strip-in-a-barrier structure.

In this Letter, the electron-blocking-layer (EBL)-free AlGaN ultraviolet (UV) light-emitting diodes (LEDs) using a strip-in-a-barrier structure have been proposed. The quantum barrier (QB) structures are systematically engineered by integrating a 1 nm intrinsic AlxGa(1-x)N strip into the middle of QBs. The resulted structures exhibit significantly reduced electron leakage and improved hole injection into the active region, thus generating higher carrier radiative recombination. Our study shows that the proposed structure improves radiative recombination by ∼220%, reduces electron leakage by ∼11 times, and enhances optical power by ∼225% at 60 mA current injection compared to a conventional AlGaN EBL LED structure. Moreover, the EBL-free strip-in-a-barrier UV LED records the maximum internal quantum efficiency (IQE) of ∼61.5% which is ∼72% higher, and IQE droop is ∼12.4%, which is ∼333% less compared to the conventional AlGaN EBL LED structure at ∼284.5nm wavelength. Hence, the proposed EBL-free AlGaN LED is the potential solution to enhance the optical power and produce highly efficient UV emitters.

Effect of step-graded superlattice electron blocking layer on performance of AlGaN based deep-UV light emitting diodes

We have presented improvement in the internal quantum efficiency (IQE) for deep-ultraviolet (DUV) AlGaN-based multi-quantum well (MQW) light-emitting diodes (LEDs) by incorporating step-graded Superlattice (SL) structure in electron-blocking layer (EBL) on AlN/sapphire template. The result shows that the UV-LED with a step-graded SL composition of AlGaN/AlGaN EBL has superior hole injection efficiency and lower electron leakage over that of the UV-LED with a conventional AlGaN EBL. Additionally, the highest IQE obtained is 37.3% which is ∼15% higher than that of the traditional AlGaN EBL at a wavelength of ∼225 nm also the efficiency droop is 22.5% which is ∼15% less compared to the conventional UV-LED structure at an injection current density of 170 A/cm2, the best values ever reported.

Performance improvement of light-emitting diodes with double superlattices confinement layer * * Project supported by the National Key Research and Development Program of China (No. 2016YFB0400102), the Beijing Municipal Science and Technology Project (Nos. Z161100002116032, D12110300140000), the National Basic Research Program of China (No. 2011CB301902), the Guangzhou Science & Technology Planning Project of Guangdong Province, China (Nos. 201604016095, 201604030035), the

In this study, the effect of double superlattices on GaN-based blue light-emitting diodes (LEDs) is analyzed numerically. One of the superlattices is composed of InGaN/GaN, which is designed before the multiple quantum wells (MQWs). The other one is AlInGaN/AlGaN, which is inserted between the last QB (quantum barriers) and p-GaN. The crucial characteristics of double superlattices LEDs structure, including the energy band diagrams, carrier concentrations in the active region, light output power, internal quantum efficiency, respectively, were analyzed in detail. The simulation results suggest that compared with the conventional AlGaN electron-blocking layer (EBL) LED, the LED with double superlattices has better performance due to the enhancement of electron confinement and the increase of hole injection. The double superlattices can make it easier for the carriers tunneling to the MQWs, especially for the holes. Furthermore, the LED with the double superlattices can effectively suppress the electron overflow out of multiple quantum wells simultaneously. From the result, we argue that output power is enhanced dramatically, and the efficiency droop is substantially mitigated when the double superlattices are used.

Numerical Investigation of InGaN Light-Emitting Diode with Al/In-Graded p-AlGaN/InGaN Superlattice Electron-Blocking Layer

Three kinds of InGaN/GaN multiple-quantum-well light-emitting diode with different electron-blocking layers (EBLs) have been investigated numerically. The energy band diagrams, light–current curves, voltage–current curves, electrostatic fields, carrier concentrations in the quantum wells, electron current densities, radiative recombination rates in active region, and internal quantum efficiency (IQE) are reported. The results show that, when the conventional AlGaN EBL is replaced by a p-AlGaN/InGaN superlattice EBL or graded p-AlyGa1−yN/InxGa1−xN superlattice EBL, respectively, the light output power at 200 mA can be increased by 46.0% and 52.8%, the turn-on voltage can be decreased from 3.2 V to 3.0 V, the IQE can be increased by 45.6% and 53.8% at 200 mA, and the efficiency droop can be reduced from 31.2% to 21.6%. These improvements are mainly attributed to the properly modified energy band structures which favor carrier injection.

Polarization-matched quaternary superlattice electron blocking layer in blue InGaN light-emitting diodes

The effect of polarization-matched AlInGaN/AlGaN superlattice (SL) electron blocking layer (EBL) on the physical characteristics of blue InGaN light-emitting diodes (LEDs) is investigated numerically. Simulation results show that the optical performance of the LEDs with polarization-matched SL EBL can be markedly improved due to the effectively suppressed polarization effect, enhanced hole injection efficiency, and reduced electron overflow. Comparing to the LEDs with conventional AlGaN EBL, an improvement of 53% in light output power is achieved for the proposed LED structure.

Electron Confinement and Hole Injection Improvement in InGaN/GaN Light-Emitting Diodes With Graded-Composition Last Quantum Barrier and Without Electron Blocking Layer

The highly magnesium (Mg)-doped wide-bandgap AlGaN electron blocking layer (EBL) is widely used in InGaN/GaN light-emitting diodes (LEDs) for electron leakage suppression. However, the EBL also reduces the hole injection efficiency and high Mg doping in AlGaN is a challenging. In this work, InGaN/GaN LEDs with a graded-composition AlGaN last quantum barrier and without the conventional AlGaN electron blocking layer were proposed and investigated numerically. Using the proposed structure, the optical output power and the efficiency droop are improved significantly when compared with the corresponding properties of conventional LEDs. The simulation results indicate that these improvements can be attributed to increments in both the electron confinement and the hole injection efficiency because of the appropriate energy band structure design of the LEDs.

Simulation Studies of InGaN Based Light-Emitting Diodes to Reduce Electron Overflow Problem by Designing Electron Blocking Layer.

InGaN/GaN-based Multi Quantum Well light-emitting diodes (MQW LEDs) with p-AlInGaN/AlGaN electron blocking layers are studied using the SimuLED simulation software for analysing the electron leakage problem. The simulation results specify the importance of p-AlInGaN/AlGaN electron blocking layers (EBL) to improve the optical and electrical performance of the LED device structure. The designed cascade AlInGaN layer in AlInGaN/AlGaN EBL was investigated by changing different Al and In concentrations and was analysed. It shows an increase in Internal Quantum Efficiency by insertion of Al(x)In(y)Ga(1-x-y)N-Al0.15Ga0.85N(X = 0.1, Y = 0.15) EBL instead of conventional AlGaN EBL. Structure shows an increasing carrier capture within active region with minimizing carrier leakage and a significant reduction in efficiency droop. The suppression in Efficiency droop phenomenon can be attributed to p-AlInGaN/AlGaN electron blocking layers which aiding a supportive barrier for electron overflow and thereby enhancing the electron blocking efficiency.

Numerical simulation of blue InGaN light-emitting diode with gradual Al and In composition p-AlInGaN electron-blocking layer

In this study, three kinds of electron-blocking layer (EBL) in blue InGaN light-emitting diodes (LEDs) are investigated numerically. They are conventional AlGaN EBL, AlInGaN EBL and gradual Al and In composition p-AlInGaN EBL. Through the analysis of the output power, internal quantum efficiency, turn-on voltage, energy band diagrams, carrier current densities and radiative recombination rates, we have got the simulation results that the LED with gradual Al and In composition p-AlInGaN EBL exhibits a higher output power, a lower electron leakage, a better hole injection efficiency and a more peaceable efficiency droop than the LED with a conventional AlGaN EBL or with a AlInGaN EBL.

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.

Polarization-Engineered High-Efficiency GaInN Light-Emitting Diodes Optimized by Genetic Algorithm

A genetic algorithm is employed to find an optimum epitaxial structure of multiple quantum wells (MQWs) and electron-blocking layer (EBL) for a GaInN-based light-emitting diode (LED). The optimized LED is composed of locally Si-doped quantum barriers (QBs) in the MQWs and a quaternary heterostructured AlGaInN EBL having a polarization-induced electric field directed oppositely to that of a conventional AlGaN EBL. The optimized LED shows 15.6% higher internal quantum efficiency, 24.6% smaller efficiency droop, and 0.21 V lower forward voltage at 200 A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> comparing to the reference LED, which has fully Si-doped QB and 20-nm-thick Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.19</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.81</sub> N EBL. We find that local Si doping near the QB/QW interface compensates the negative polarization-induced sheet charge at the interface and reduces electric field in the QWs, thereby enhancing electron-hole wave function overlap. In addition, the inverted polarization field in the quaternary EBL provides a high barrier for electrons but a low barrier for holes, resulting in enhanced electron-blocking and hole-injection characteristics.

Engineering the carrier dynamics of InGaN nanowire white light-emitting diodes by distributed p-AlGaN electron blocking layers.

We report on the demonstration of a new type of axial nanowire LED heterostructures, with the use of self-organized InGaN/AlGaN dot-in-a-wire core-shell nanowire arrays. The large bandgap AlGaN shell is spontaneously formed on the sidewall of the nanowire during the growth of AlGaN barrier of the quantum dot active region. As such, nonradiative surface recombination, that dominates the carrier dynamics of conventional axial nanowire LED structures, can be largely eliminated, leading to significantly increased carrier lifetime from ~0.3 ns to 4.5 ns. The luminescence emission is also enhanced by orders of magnitude. Moreover, the p-doped AlGaN barrier layers can function as distributed electron blocking layers (EBLs), which is found to be more effective in reducing electron overflow, compared to the conventional AlGaN EBL. The device displays strong white-light emission, with a color rendering index of ~95. An output power of >5 mW is measured for a 1 mm × 1 mm device, which is more than 500 times stronger than the conventional InGaN axial nanowire LEDs without AlGaN distributed EBLs.

Advantages of GaN-Based Light-Emitting Diodes With Polarization-Reduced Chirped Multiquantum Barrier

The advantages of GaN-based light-emitting diodes with polarization-reduced chirped multiquantum barrier (PR-CMQB) as electron blocking layer (EBL) are investigated numerically and experimentally. Both simulation and experiment results indicate that the LED with PR-CMQB possesses higher internal quantum efficiency and light output power as compared with its counterparts with either conventional single AlGaN EBL or CMQB. These improvements are mainly attributed to the suppression of electron leakage and the enhancement of hole injection efficiency. Furthermore, the efficiency droop is markedly reduced when the PR-CMQB is employed.

Improving hole injection efficiency by manipulating the hole transport mechanism through p-type electron blocking layer engineering.

The p-type AlGaN electron blocking layer (EBL) is widely used in InGaN/GaN light-emitting diodes (LEDs) for electron overflow suppression. However, a typical EBL also reduces the hole injection efficiency, because holes have to climb over the energy barrier generated at the p-AlGaN/p-GaN interface before entering the quantum wells. In this work, to address this problem, we report the enhancement of hole injection efficiency by manipulating the hole transport mechanism through insertion of a thin GaN layer of 1nm into the p-AlGaN EBL and propose an AlGaN/GaN/AlGaN-type EBL outperforming conventional AlGaN EBLs. Here, the position of the inserted thin GaN layer relative to the p-GaN region is found to be the key to enhancing the hole injection efficiency. InGaN/GaN LEDs with the proposed p-type AlGaN/GaN/AlGaN EBL have demonstrated substantially higher optical output power and external quantum efficiency.

Effects of the p-AlInGaN/GaN superlattices' structure on the performance of blue LEDs

The advantages of the p-AlInGaN/GaN superlattices' (SLs) structure as an electron blocking layer (EBL) for InGaN blue light-emitting diodes (LEDs) were studied by experiment and APSYS simulation. Electroluminescence (EL) measurement results show that the LEDs with the p-AlInGaN/GaN SLs' structure EBL exhibited better optical performance compared with the conventional AlGaN EBL due to the enhancement of hole concentration and hole carrier transport efficiency, and the confinement of electrons' overflow between multiple quantum-wells (MQWs) and EBL.

Advantages of Blue LEDs With Graded-Composition AlGaN/GaN Superlattice EBL

InGaN/GaN light-emitting diodes (LEDs) with graded-composition AlGaN/GaN superlattice (SL) electron blocking layer (EBL) were designed and grown by metal-organic chemical vapor deposition. The simulation results demonstrated that the LED with a graded-composition AlGaN/GaN SL EBL have superior hole injection efficiency and lower electron leakage over the LED with a conventional AlGaN EBL or normal AlGaN/GaN SL EBL. Therefore, the efficiency droop can be alleviated to be ~ 20% from maximum at an injection current of 15-120 mA, which is smaller than that for conventional AlGaN EBL (30%). The corresponding experimental results also confirm that the use of a graded-composition AlGaN/GaN SL EBL can markedly enhance the light output power by 60%.