Superlattice Electron Blocking Layer Research Articles

AlGaN-Based Deep UV Communication LED With Superlattice Electron-Blocking Layer at 274 nm

AlGaN-Based Deep UV Communication LED With Superlattice Electron-Blocking Layer at 274 nm

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%.

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.

Study of ultraviolet light emitting diodes with InGaN quantum dots and lattice matched superlattice electron blocking layers.

Ultraviolet light emitting diodes (UV-LEDs) face the challenges including insufficient hole injection and severe electron leakage. Quantum dots (QDs) have been proven to provide three-dimensionally localized states for carriers, thereby enhancing carrier confinement. Therefore, UV-LEDs employing InGaN QDs are designed and studied in this paper. The APSYs software is used to simulate UV-LEDs. Simulation results indicate that the QDs effectively improve the electron and hole concentration in the active region. However, UV-LEDs with QDs experience efficiency droop due to serious electron leakage. What's more, the lattice mismatch between last quantum barrier (LQB) and electron blocking layer (EBL) leads to the polarization field, which induces the downward band bending at the LQB/EBL interface and reduces effective barrier height of EBL for electrons. The AlInGaN/AlInGaN lattice matched superlattice (LMSL) EBL is designed to suppress electron leakage while mitigating lattice mismatch between LQB and EBL. The results indicate that the utilization of QDs and LMSL EBL contributes to increasing the electron and hole concentration in the active region, reducing electron leakage, enhancing radiative recombination rate, and reducing turn-on voltage. The efficiency droop caused by electron leakage is mitigated. When the injection current is 120 mA, the external quantum efficiency is increased to 9.3% and the output power is increased to 38.3 mW. This paper provides a valuable reference for addressing the challenges of insufficient hole injection and severe electron leakage.

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.

Research on the Electron-blocking Layers in the GaN-based LEDs

The electron overflow happening in the active region of GaN-based light-emitting diodes (LEDs) will decrease the rate of radiative recombination, leading to a reduction of light output power. To deal with the problem, the electron blocking layer(EBL) is designed to weaken electrons leakage. Various designs and structures of the electron blocking layers embedded in the multiple quantum layers of GaN-based LEDs are reviewed in this paper. Designs such as trapezoidal EBL, step-graded superlattice EBL, and hybrid EBL can all effectively limit the amount of electron overflow. With many designs of EBL, LEDs are expected to have a wider range of applications in the opto-electric field.

Improving Charge Carrier Transport Properties in AlGaN Deep Ultraviolet Light Emitters Using Al-Content Engineered Superlattice Electron Blocking Layer

In this study, we investigate a unique Al-content engineered superlattice electron blocking layer (AESL-EBL) for improving the charge carrier transport properties of AlGaN quantum well (QW) deep ultraviolet (DUV) light-emitting diode (LED) structures. LED structures without EBL, with conventional bulk EBL (BEBL), and superlattice EBL (SL-EBL) are used for comparison. It is found that the LED structure with the AESL-EBL can exhibit superior electron blocking and hole injection, leading to reduced efficiency droop and improved light output power, compared to LED structures without EBL and with BEBL. Notably, the LED structure with AESL-EBL also outperforms the LED structure with SL-EBL, benefitting from the Al-content engineered SL. In the end, such an ASEL-EBL is applied to a DUV laser diode structure, and by optimizing the device structure low Mg-induced internal loss of around 1 cm−1 can be obtained.

Performance Enhancement of Algan-Based Deep Ultraviolet Laser Diodes with Step Superlattice Electron Blocking Layer and Wedge-Shaped Hole Blocking Layer

Performance Enhancement of Algan-Based Deep Ultraviolet Laser Diodes with Step Superlattice Electron Blocking Layer and Wedge-Shaped Hole Blocking Layer

Intelligent optimization design of electron barrier layer for AlGaN-based deep-ultraviolet light-emitting diodes

AlGaN-based deep-ultraviolet light-emitting diodes (DUV LEDs) are widely used in sterilization, sensing, water purification, medical treatment, non-line of sight (NLOS) communication and many other fields. Especially it has been reported that the global novel coronavirus (COVID-19) can be effectively inactivated by the DUV light with a wavelength below 280 nm (UVC) within a few seconds, which has also attracted great attention. However, the external quantum efficiency (EQE) of UVC LED is still at a low level, generally not more than 10%. As an important component of EQE, internal quantum efficiency (IQE) plays a crucial role in realizing high-performance DUV-LED. In order to improve the IQE of AlGaN-based DUV-LED, this work adopts an electron blocking layer (EBL) structure based on InAlGaN/AlGaN superlattice. The results show that the superlattice EBL structure can effectively improve the IQE compared with the traditional single-layer and double-layer EBL structure for the DUV-LED. On this basis, the optimization method based on JAYA intelligent algorithm for LED structure design is proposed in this work. Using the proposed design method, the InAlGaN/AlGaN superlattice EBL structure is further optimized to maximize the LED’s IQE. It is demonstrated that the optimized superlattice EBL structure is beneficial to not only the suppression of electron leakage but also the improvement of hole injection, leading to the increase of carrier recombination in the active region. As a result, the IQE of the DUV-LED at 200 mA injection current is 41.2% higher than that of the single-layer EBL structure. In addition, the optimized structure reduces IQE at high current from 25% to 4%. The optimization method based on intelligent algorithm can break through the limitation of the current LED structure design and provide a new method to improve the efficiency of AlGaN-based DUV-LED.

AlGaN-Based Deep-Ultraviolet Laser Diodes with Novel Superlattice Electron-Blocking Layers

AlGaN-Based Deep-Ultraviolet Laser Diodes with Novel Superlattice Electron-Blocking Layers

High Performance of a Non-Polar AlGaN-Based DUV-LED with a Quaternary Superlattice Electron Blocking Layer

High Performance of a Non-Polar AlGaN-Based DUV-LED with a Quaternary Superlattice Electron Blocking Layer

Optimization of AlGaN-Based Deep Ultraviolet Laser Diodes with Graded Rectangular Superlattice Electron Blocking Layer and Graded Trapezoidal Superlattice Hole Blocking Layer

To improve the carrier confinement capability and optimize the performance of deep ultraviolet laser diodes (DUV-LDs), we propose the graded rectangular superlattice (GRSL) electron blocking layer (EBL) and the graded trapezoidal superlattice (GTSL) hole blocking layer (HBL) in this paper. Crosslight software is used to simulate and compare the DUV-LDs with rectangular superlattice (RSL) EBL and RSL HBL, GRSL EBL and GRSL HBL, and GRSL EBL and GTSL HBL. The simulation results indicate that GRSL EBL and GTSL HBL increase the carrier concentration in the quantum wells, reduce the electron leakage in the p-type region and the hole leakage in the n-type region, increase the radiation recombination rate, reduce the threshold voltage and threshold current, and increase the electro-optical conversion efficiency and output power of DUV-LDs more effectively.

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.

High-performance AlGaN-based deep ultraviolet light-emitting diodes with different types of InAlGaN/AlGaN electron blocking layer

The efficiency performance of AlGaN-based deep ultraviolet light-emitting diodes (DUV LEDs) is restricted by the poor hole injection and severe electron leakage. Here, we propose two types of electron blocking layer (EBL), including InAlGaN/AlGaN EBL and InAlGaN/AlGaN superlattice EBL, to enhance the carrier injection efficiency. We numerically simulated the effect of InAlGaN-based EBL on effective barrier height for carriers. The simulation results reveal that the effective barrier height for carriers can be modulated to be beneficial for electron blocking and hole injection by optimizing In-composition. As a result, the 272 nm DUV LED with InAlGaN/AlGaN EBL exhibits better performance, compared to the DUV LED with AlGaN EBL. What is more, device performance can be further improved when the InAlGaN/AlGaN EBL is replaced by InAlGaN/AlGaN superlattice EBL, due to the latter is more effective to modulate the effective barrier height for carriers when the In-composition is appropriate.

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 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.

Design and Optimization of Electron-Blocking Layer in Deep Ultraviolet Light-Emitting Diodes

Optical and electrical performance and the relevant physical properties of deep ultraviolet (DUV) AlGaN-based light-emitting diodes (LEDs) are numerically investigated. The influence of bulk AlGaN electron-blocking layer (EBL) with various Al compositions and Mg-doping concentrations on the output performance of DUV LEDs is systemically explored. Simulation results show that the DUV LED with bulk Al0.85Ga0.15N EBL with a relatively low Mg-doping concentration of $2\times 10^{19}$ cm−3 may have high wall-plug efficiency. The LED structure with Al0.55Ga0.45N/Al0.75Ga0.25N superlattice (SL) EBL is proposed in this study, which is shown to have high wall-plug efficiency similar to the LED with bulk Al0.85Ga0.15N EBL while the Al composition of AlGaN EBL can be effectively reduced. The proposed LED structure with SL EBL provides a practical way to fabricate high-crystalline-quality and high-efficiency DUV LEDs.

Monolithic integration of GaN-based phototransistors and light-emitting diodes.

Monolithic integration of GaN-based phototransistors and light-emitting diodes (LEDs) is reported. Starting with an LED epitaxial wafer, selective Si diffusion was performed to produce an n-p-i-n structure for the phototransistor. A traditional AlGaN bulk electron-blocking layer (EBL) can block electron injection from an emitter to a collector, thereby hindering the photocurrent amplification process. We used an LED wafer with a superlattice EBL; blocking can be removed under a bias of approximately 7 V and above. External quantum efficiencies of more than 100% and 600% at approximately 380 nm and 330 nm, respectively, were achieved at room temperature and a bias of 11 V, corresponding to responsivities of 0.31 and 1.6 A/W, respectively, significantly higher than commercially available ultraviolet (UV) detectors. Furthermore, we demonstrated an integrated operation of the device. UV light was detected using a phototransistor that sent signals to drive an integrated LED as an indicator.