Performance enhancement of blue light-emitting diodes by adjusting the p-type doped last barrier

Blue light-emitting diodes (LEDs) with different p-doping concentrations in the last barrier have been studied numerically. The energy band diagrams, carrier concentrations, internal quantum efficiency and light output power are investigated using APSYS software. The simulation results show that the LED structure with p-doping in the last barrier has a better hole-injection efficiency and confinement of electron leakage over the structure with the last undoped GaN barrier due to enhancement of the holes’ injection and the electrons’ confinement. As a result, the efficiency droop is markedly improved, and the light output power is greatly enhanced when a larger p-doping amount is centralised in the last barrier.     

Efficiency enhancement of ultraviolet light-emitting diodes with segmentally graded p-type AlGaN layer

AlGaN-based ultraviolet light-emitting diodes(UV-LEDs) have attracted considerable interest due to their wide range of application fields. However, they are still suffering from low light out power and unsatisfactory quantum efficiency.The utilization of polarization-doped technique by grading the Al content in p-type layer has demonstrated its effectiveness in improving LED performances by providing sufficiently high hole concentration. However, too large degree of grading through monotonously increasing the Al content causes strains in active regions, which constrains application of this technique, especially for short wavelength UV-LEDs. To further improve 340-nm UV-LED performances, segmentally graded Al content p-Al_xGa_(1-x)N has been proposed and investigated in this work. Numerical results show that the internal quantum efficiency and output power of proposed structures are improved due to the enhanced carrier concentrations and radiative recombination rate in multiple quantum wells, compared to those of the conventional UV-LED with a stationary Al content AlGaN electron blocking layer. Moreover, by adopting the segmentally graded p-Al_xGa_(1-x)N, band bending within the last quantum barrier/p-type layer interface is effectively eliminated.     

Suppression of electron and hole overflow in GaN-based near-ultraviolet laser diodes

In order to suppress the electron leakage to p-type region of near-ultraviolet GaN/In_xGa_(1-x )N/GaN multiple-quantumwell(MQW) laser diode(LD), the Al composition of inserted p-type AlxGa_(1-x)N electron blocking layer(EBL) is optimized in an effective way, but which could only partially enhance the performance of LD. Here, due to the relatively shallow GaN/In_(0.04)Ga_(0.96)N/GaN quantum well, the hole leakage to n-type region is considered in the ultraviolet LD. To reduce the hole leakage, a 10-nm n-type Al_xGa_(1-x)N hole blocking layer(HBL) is inserted between n-type waveguide and the first quantum barrier, and the effect of Al composition of Al_xGa_(1-x)N HBL on LD performance is studied. Numerical simulations by the LASTIP reveal that when an appropriate Al composition of Al_xGa_(1-x)N HBL is chosen, both electron leakage and hole leakage can be reduced dramatically, leading to a lower threshold current and higher output power of LD.     

Performance Improvement of GaN-Based Violet Laser Diodes

The influences of InGaN/GaN multiple quantum wells(MQWs) and AlGaN electron-blocking layers(EBL) on the performance of GaN-based violet laser diodes are investigated. Compared with the InGaN/GaN MQWs grown at two different temperatures, the same-temperature growth of InGaN well and GaN barrier layers has a positive effect on the threshold current and slope efficiency of laser diodes, indicating that the quality of MQWs is improved. In addition, the performance of GaN laser diodes could be further improved by increasing Al content in the AlGaN EBL due to the fact that the electron leakage current could be reduced by properly increasing the barrier height of AlGaN EBL. The violet laser diode with a peak output power of 20 W is obtained.     

Enhanced performance of AlGaN-based ultraviolet light-emitting diodes with linearly graded AlGaN inserting layer in electron blocking layer

The conventional stationary Al content Al GaN electron blocking layer(EBL) in ultraviolet light-emitting diode(UV LED) is optimized by employing a linearly graded Al Ga N inserting layer which is 2.0 nm Al_(0.3) Ga_(0.7) N/5.0 nm Alx Ga_(1-x) N/8.0 nm Al_(0.3) Ga_(0.7) N with decreasing value of x. The results indicate that the internal quantum efficiency is significantly improved and the efficiency droop is mitigated by using the proposed structure. These improvements are attributed to the increase of the effective barrier height for electrons and the reduction of the effective barrier height for holes,which result in an increased hole injection efficiency and a decreased electron leakage into the p-type region. In addition,the linearly graded AlGaN inserting layer can generate more holes in EBL due to the polarization-induced hole doping and a tunneling effect probably occurs to enhance the hole transportation to the active regions, which will be beneficial to the radiative recombination.     

Numerical study of performance characteristics of deep violet InGaN DQW laser diodes with AlInGaN quaternary multi quantum barrier electron blocking layer

The performance characteristics of deep violet In_0.082Ga_0.918N/GaN double quantum well (DQW) laser diodes (LDs) with different electron blocking layer (EBL) including a ternary AlGaN bulk EBL, a quaternary AlInGaN bulk EBL and ternary AlGaN multi quantum barrier (MQB) EBL has been numerically investigated. Inspired by the abovementioned structures, a new LD structure with a quaternary AlInGaN MQB EBL has been proposed to improve the performance characteristics of the deep violet InGaN DQW LDs. Simulation results indicated that the LD structure with the quaternary AlInGaN MQB EBL present the highest output power, slope efficiency and differential quantum efficiency (DQE) and lowest threshold current compared with the above mentioned structures. They also indicated that choosing an appropriate aluminum (Al) and indium (In) composition in the quaternary AlInGaN MQB layers could control both piezoelectric and spontaneous polarizations. It will decrease the electron overflow from the active region to p-side and increased the contribution of electron and hole carriers to the radiative recombination effectively. Enhancing radiative recombination in the well using the quaternary AlInGaN MQB EBL also increased the optical output power and optical intensity.     

GaN/In_xGa_(1-x)N型最后一个量子势垒对发光二极管内量子效率的影响

GaN/In_xGa_(1-x)N型最后一个量子势垒结构能有效提高发光二极管(LED)器件内量子效率,缓解LED效率随输入电流增大而衰减的问题.本文综述了该结构及其结构变化——In组分梯度递增以及渐变、GaN/In_xGa_(1-x)N界面极化率改变等对改善LED器件性能的影响及优势,归纳总结了不同结构的GaN/In_xGa_(1-x)N型最后一个量子垒的工作机理,阐明极化反转是该结构提高LED性能的根本原因.在综述该结构发展的基础之上,通过APSYS仿真计算,进一步探索和深入分析了该结构中In_xGa_(1-x)N层的In组分及其厚度变化对LED内量子效率的影响.结果表明:In组分的增加有助于在GaN/In_xGa_(1-x)N界面产生更多的极化负电荷,增加GaN以及电子阻挡层处导带势垒高度,减少电子泄漏,从而提高LED的内量子效率;但GaN/In_xGa_(1-x)N型最后一个量子势垒中In_xGa_(1-x)N及GaN层厚度的变化由于会同时引起势垒高度和隧穿效应的改变,因而In_xGa_(1-x)N和GaN层的厚度存在一个最佳比值以实现最大化的减小漏电子,提高内量子效率.     

Performance characteristics of deep violet InGaN DQW laser diodes with InGaN/GaN superlattice waveguide layers

The effect of the indium (In) composition of In_xGa_1−xN (GaN) waveguide layers on the performance of deep violet In_0.082Ga_0.918N/GaN double quantum well (DQW) laser diodes (LDs) emitting at 390 nm output emission wavelength has been numerically investigated. Simulation results indicated that by increasing In composition of the In_xGa_1−xN waveguide layers, the threshold current decreases, the slope efficiency, and differential quantum efficiency (DQE) increase, whereas the output power decreases. The increase in the In composition of the InGaN waveguide layers increases the refractive index and consequently increases the optical confinement factor (OCF) which result in the increase in the slope efficiency and DQE and the decrease in the threshold current. The decreasing movement of electron and hole carriers from the bulk waveguide layers to the active regions also causes to decrease the output power. A new LD structure with InGaN/GaN superlattice (SL) waveguide layers has been proposed to exploit the increased OCF of InGaN waveguide structures, and the enhanced electron and hole mobilities and the tunneling effect of the periodic structure of the SL structures. The results also showed that the use of InGaN/GaN SL waveguide structures effectively improves the output power, slope efficiency and DQE and decreases the threshold current of the LD compared with (In)GaN bulk waveguide structure.     

量子垒高度对深紫外LED调制带宽的影响

AlGaN基深紫外LED由于具有高调制带宽和小芯片尺寸,在紫外光通信领域受到越来越多的关注.本研究通过改变生长AlGaN量子垒层的Al源流量,生长了三种具有不同量子垒高度的深紫外LED,研究了量子垒高度对深紫外LED光电特性和调制特性的影响.研究发现,随着量子垒高度的增加,深紫外LED的光功率出现先增加后减小的趋势,量...     

Efficiency enhancement of an InGaN light-emitting diode with a p-AlGaN/GaN superlattice last quantum barrier

In this study,the efficiency droop of an InGaN light-emitting diode(LED)is reduced significantly by using a pAlGaN/GaN superlattice last quantum barrier.The reduction in efficiency droop is mainly caused by the decrease of electron current leakage and the increase of hole injection efficiency,which is revealed by investigating the light currents,internal quantum efficiencies,energy band diagrams,carrier concentrations,carrier current densities,and radiative recombination efficiencies of three LED structures with the advanced physical model of semiconductor device(APSYS).     

GaN/AlGaN双带红外探测及光子频率上转换研究

研究了GaN/AlGaN异质结构中的双带（中、远）红外探测及光子频率上转换特性.通过光致发光光谱确认GaN/AlGaN探测器结构中AlGaN本征层的Al组分,讨论了不同Al组分GaN/AlGaN异质结的导带带阶界面功函数差.在拟合单周期GaN/AlGaN探测器中红外和远红外波段响应谱的基础上,研究多周期GaN/AlGaN探测器与GaN/AlGaN发光二极管集成结构的中红外和远红外光子频率上转换效率与GaN发射层厚度、AlGaN本征层厚度、紫光光子出射效率、内量子效率、空间频率和发射层掺杂浓度间的关系,优化 关键词： 双带红外探测 光子频率上转换 响应谱 GaN/AlGaN     

A dual-blue light-emitting diode based on strain-compensated InGaN-AlGaN/GaN quantum wells

A strain-compensated InGaN quantum well(QW) active region employing a tensile AlGaN barrier is analyzed.Its spectral stability and efficiency droop for a dual-blue light-emitting diode(LED) are improved compared with those of the conventional InGaN/GaN QW dual-blue LEDs based on a stacking structure of two In0.18Ga0.82N/GaN QWs and two In0.12Ga0.88N/GaN QWs on the same sapphire substrate.It is found that the optimal performance is achieved when the Al composition of the strain-compensated AlGaN layer is 0.12 in blue QW and 0.21 in blue-violet QW.The improvement performance can be attributed to the strain-compensated InGaN-AlGaN/GaN QW,which can provide a better carrier confinement and effectively reduce leakage current.     

Improved performance of InGaN light-emitting diodes with a novel sawtooth-shaped electron blocking layer

A sawtooth-shaped electron blocking layer is proposed to improve the performance of light-emitting diodes （LEDs）. The energy band diagram, the electrostatic field in the quantum well, the carrier concentration, the electron leakage, and the internal quantum efficiency are systematically studied. The simulation results show that the LED with a sawtooth-shaped electron blocking layer possesses higher output power and a smaller efficiency droop than the LED with a conventional A1GaN electron blocking layer, which is because the electron confinement is enhanced and the hole injection efficiency is improved by the appropriately modified electron blocking layer energy band.     

Impact of AlxGa1-xN barrier thickness and Al composition on electrical properties of ferroelectric HfZrO/Al2O3/AlGaN/GaN MFSHEMTs

Ferroelectric (FE) HfZrO/Al$_{2}$O$_{3}$ gate stack AlGaN/GaN metal-FE-semiconductor heterostructure high-electron mobility transistors (MFSHEMTs) with varying Al$_{x}$Ga$_{1-x}$N barrier thickness and Al composition are investigated and compared by TCAD simulation with non-FE HfO$_{2}$/Al$_{2}$O$_{3}$ gate stack metal-insulator-semiconductor heterostructure high-electron mobility transistors (MISHEMTs). Results show that the decrease of the two-dimensional electron gas (2DEG) density with decreasing AlGaN barrier thickness is more effectively suppressed in MFSHEMTs than that in MISHEMTs due to the enhanced FE polarization switching efficiency. The electrical characteristics of MFSHEMTs, including transconductance, subthreshold swing, and on-state current, effectively improve with decreasing AlGaN thickness in MFSHEMTs. High Al composition in AlGaN barrier layers that are under 3-nm thickness plays a great role in enhancing the 2DEG density and FE polarization in MFSHEMTs, improving the transconductance and the on-state current. The subthreshold swing and threshold voltage can be reduced by decreasing the AlGaN thickness and Al composition in MFSHEMTs, affording favorable conditions for further enhancing the device.     

反射式GaN光电阴极表面势垒对量子效率衰减的影响

针对反射式GaN光电阴极长波段量子效率衰减较大, 短波段量子效率衰减较小的实验现象, 在考虑谷间散射的情况下, 利用玻尓兹曼分布和基于Airy函数的传递矩阵法, 计算了发射电子能量分布, 分析了表面势垒变化对量子效率衰减的影响, 理论与实验符合较好. 激活层有效偶极子数的减少使表面势垒宽度和高度增加, 引起长波光子激发产生的发射电子能量分布衰减较大, 短波光子激发产生的发射电子能量分布衰减较小, 这是量子效率在长波段衰减较大, 短波段衰减较小的根本原因.     

Improvement of characteristics of InGaN light-emitting diode by using a staggered AlGaN electron-blocking layer

The optical and physical properties of InGaN light-emitting diode (LED) with a specific design of staggered AlGaN electron-blocking layer (EBL) are investigated numerically in detail. The electrostatic field distribution, energy band, carrier concentration, electroluminescence (EL) intensity, internal quantum efficiency (IQE), and the output power are simulated. The results reveal that this specific design has a remarkable improvement of optical performance compared with the design of conventional LED. The lower electron leakage current, higher hole injection efficiency, and consequently mitigated efficiency droop are achieved. The significant decrease of electrostatic field at the interface between the last barrier and the EBL of LED could be one of the main reasons for these improvements.     

Improvement of characteristics of an InGaN light-emitting diode by using a staggered AlGaN electron-blocking layer

The optical and physical properties of an InGaN light-emitting diode (LED) with a specific design of a staggered AlGaN electron-blocking layer (EBL) are investigated numerically in detail. The electrostatic field distribution, energy band, carrier concentration, electroluminescence (EL) intensity, internal quantum efficiency (IQE), and the output power are simulated. The results reveal that this specific design has a remarkable improvement in optical performance compared with the design of a conventional LED. The lower electron leakage current, higher hole injection efficiency, and consequently mitigated efficiency droop are achieved. The significant decrease of electrostatic field at the interface between the last barrier and the EBL of the LED could be one of the main reasons for these improvements.     

Investigation of blue InGaN light-emitting diodes with p-AlGaN/InGaN superlattice interlayer

The blue InGaN light-emitting diodes (LEDs), employing a lattice-compensated p-AlGaN/InGaN superlattice (SL) interlayer to link the last quantum barrier and electron blocking layer (EBL), are proposed and investigated numerically. The simulation results indicate that the newly designed LEDs have better hole injection efficiency, lower electron leakage, and smaller electrostatic fields in the active region over the conventional LEDs mainly attributed to the mitigated polarization-induced downward band bending. Furthermore, the markedly improved output power and efficiency droop are also suggested when the conventional LEDs corresponding to experiment data are replaced by the newly designed LEDs.     

High-efficiency InGaN/AlInGaN multiple quantum wells with lattice-matched AlInGaN superlattices barrier

A new approach to fabricating high-quality AlInGaN film as a lattice-matched barrier layer in multiple quantum wells(MQWs) is presented. The high-quality AlInGaN film is realized by growing the AlGaN/InGaN short period superlattices through metalorganic chemical vapor deposition, and then being used as a barrier in the MQWs. The crystalline quality of the MQWs with the lattice-matched AlInGaN barrier and that of the conventional InGaN/GaN MQWs are characterized by x-ray diffraction and scanning electron microscopy. The photoluminescence(PL) properties of the InGaN/AlInGa N MQWs are investigated by varying the excitation power density and temperature through comparing with those of the InGaN/GaN MQWs. The integral PL intensity of InGaN/AlInGaN MQWs is over 3 times higher than that of InGaN/GaN MQWs at room temperature under the highest excitation power. Temperature-dependent PL further demonstrates that the internal quantum efficiency of InGaN/AlInGaN MQWs(76.1%) is much higher than that of InGaN/GaN MQWs(21%).The improved luminescence performance of InGaN/AlInGaN MQWs can be attributed to the distinct reduction of the barrier-well lattice mismatch and the strain-induced non-radiative recombination centers.     

Dual-blue light-emitting diode based on strain-compensated InGaN-AlGaN/GaN quantum wells

Strain-compensated InGaN quantum well (QW) active region employing tensile AlGaN barrier is analyzed. Its spectral stability and efficiency droop for dual-blue light-emitting diode (LED) are improved compared with those of the conventional InGaN/GaN QW dual-blue LED based on stacking structure of two In_0.18Ga_0.82N/GaN QWs and two In_0.12Ga_0.88N/GaN QWs on the same sapphire substrate. It is found that the optimal performance is achieved when the Al composition of strain-compensated AlGaN layer is 0.12 in blue QW and 0.21 in blue-violet QW. The improvement performance can be attributed to the strain-compensated InGaN-AlGaN/GaN QW that can provide a better carrier confinement and effectively reduce leakage current.