多量子势垒双阻挡层结构对AlGaN 基深紫外激光二极管的性能优化

为提高AlGaN基深紫外激光二极管(Deep Ultraviolet Laser Diodes,DUV-LD)有源区内载流子浓度,减少载流子泄露,提出一种DUV-LD双阻挡层结构,相对于传统的单一电子阻挡层(Electron Blocking Layer, EBL)结构,又引入一空穴阻挡层(Hole Blocking Layer, HBL),仿真结果证明空穴阻挡层的应用能很好地减少空穴泄漏.同时又对双阻挡层改用五周期Al_0.98Ga_0.02N/Al_0.9Ga_0.1N多量子势垒层结构,结果显示与矩形EBL和HBL激光二极管相比,多量子势垒EBL和HBL激光二极管有更好的斜率效率,并且有源区内电子和空穴载流子浓度以及辐射复合速率都有效提高,其中多量子势垒EBL在阻挡电子泄露方面效果更显著.     

Enhanced carrier injection in InGaN/GaN multiple quantum wells LED with polarization-induced electron blocking barrier

In this report, we designed a light emitting diode (LED) structure in which an N-polar p-GaN layer is grown on top of Ga-polar In_0.1Ga_0.9N/GaN quantum wells (QWs) on an n-GaN layer. Numerical simulation reveals that the large polarization field at the polarity inversion interface induces a potential barrier in the conduction band, which can block electron overflow out of the QWs. Compared with a conventional LED structure with an Al_0.2Ga_0.8N electron blocking layer (EBL), the proposed LED structure shows much lower electron current leakage, higher hole injection, and a significant improvement in the internal quantum efficiency (IQE). These results suggest that the polarization induced barrier (PIB) is more effective than the AlGaN EBL in suppressing electron overflow and improving hole transport in GaN-based LEDs.     

Improvement of radiative recombination rate in deep ultraviolet laser diodes with step-like quantum barrier and aluminum-content graded electron blocking layer

The design of the active region structures, including the modifications of structures of the quantum barrier(QB) and electron blocking layer(EBL), in the deep ultraviolet(DUV) Al Ga N laser diode(LD) is investigated numerically with the Crosslight software. The analyses focus on electron and hole injection efficiency, electron leakage, hole diffusion,and radiative recombination rate. Compared with the reference QB structure, the step-like QB structure provides high radiative recombination and maximum output power. Subsequently, a comparative study is conducted on the performance characteristics with four different EBLs. For the EBL with different Al mole fraction layers, the higher Al-content Al Ga N EBL layer is located closely to the active region, leading the electron current leakage to lower, the carrier injection efficiency to increase, and the radiative recombination rate to improve.     

Performance enhancement of InGaN light-emitting diodes with a leakage electron recombination quantum well

An InGaN light-emitting diodes with a leakage electron recombination (LER) quantum well have been proposed and investigated numerically by using the APSYS simulation software. The simulation results indicate that the AlGaN electron blocking layer inserted between the last two quantum wells changed the carrier concentrations distribution, and the leakage electrons can be further recombined with holes in the LER quantum well which can decrease the electrons that spill out from active region. As a result, the internal quantum efficiency and light output power are markedly improved attributed to LER quantum well.     

Comparison of nitride-based dual-wavelength light- emitting diodes with an InAlN electron-blocking layer and with p-type doped barriers

The advantages of nitride-based dual-wavelength light-emitting diodes (LEDs) with an InAlN electron blocking layer (EBL) are studied. The emission spectra,carrier concentration in the quantum wells (QWs),energy band and internal quantum efficiency (IQE) are investigated. The simulation results indicate that an LED with an InAlN EBL performs better over a conventional LED with an AlGaN EBL and an LED with p-type-doped QW barriers. All of the advantages are due to the enhancement of carrier confinement and the lower electron leakage current. The simulation results also show that the efficiency droop is markedly improved and the luminous intensity is greatly enhanced when an InAlN EBL is used.     

Improved performance of near UV light-emitting diodes with a composition-graded p-AlGaN irregular sawtooth electron-blocking layer

We investigate the performances of the near-ultraviolet(about 350 nm-360 nm) light-emitting diodes(LEDs) each with specifically designed irregular sawtooth electron blocking layer(EBL) by using the APSYS simulation program.The internal quantum efficiencies(IQEs),light output powers,carrier concentrations in the quantum wells,energy-band diagrams,and electrostatic fields are analyzed carefully.The results indicate that the LEDs with composition-graded pAl_xGa_(1-x)N irregular sawtooth EBLs have better performances than their counterparts with stationary component p-AlGaN EBLs.The improvements can be attributed to the improved polarization field in EBL and active region as well as the alleviation of band bending in the EBL/p-AlGaN interface,which results in less electron leakage and better hole injection efficiency,thus reducing efficiency droop and enhancing the radiative recombination rate.     

利用W形空穴阻挡层降低AlGaN基深紫外激光二极管的空穴泄露

本文设计了V形和W形的空穴阻挡层(HBL)结构,改善空穴在AlGaN基深紫外激光二极管(DUV-LD)n型区的泄露问题.使用Crosslight软件,将参考型矩形、V形和W形三种空穴阻挡层结构进行仿真研究,分别比较了三种不同结构的DUV-LD能带、n区空穴浓度、辐射复合率、电光转换效率、有源区载流子浓度等特性,结果表明,具有W形空穴阻挡层的DUV-LD拥有更高的空穴有效势垒高度、更高的辐射复合率、更低的空穴泄露以及更好的斜率效率,可以有效降低深紫外激光二极管在n型区的空穴泄露,提升其光学和电学性能.     

GaNAs/GaAs量子阱的激子局域化以及退局域化

我们利用光荧光(PL)以及时间分辨光谱(TRPL)研究了用MBE生长在GaAs衬底上的GaNAs/GaAs量子阱的激子局域化以及退局域化.研究发现,在低温下用连续光(Cw)激发,由于GaNAs中势振荡所产生的局域激子发光是所测量到光谱的主要发光来源.然而在脉冲激发下,情况完全不同.在高载流子密度激发或者高温下GaNAs/GaAs量子阱中例外,一个高能端的PL峰成为了主要的发光来源.通过研究,我们将这个新的发光峰指认为量子阱中非局域激子复合的PL峰.这个发光峰在温度和激发强度的变化过程中与局域激子相互竞争.我们相信这一过程也是许多文献所报道的在InGaN和AlGaN等氮化物中经常观测到的发光峰位随温度"S"形变化的主要根源.     

GaNAs/GaAs量子阱的激子局域化以及退局域化

我们利用光荧光(PL)以及时间分辨光谱(TRPL)研究了用MBE生长在GaAs衬底上的GaNAs/GaAs量子阱的激子局域化以及退局域化。研究发现,在低温下用连续光(CW)激发,由于GaNAs中势振荡所产生的局域激子发光是所测量到光谱的主要发光来源。然而在脉冲激发下,情况完全不同。在高载流子密度激发或者高温下GaNAs/GaAs量子阱中例外,一个高能端的PL峰成为了主要的发光来源。通过研究,我们将这个新的发光峰指认为量子阱中非局域激子复合的PL峰。这个发光峰在温度和激发强度的变化过程中与局域激子相互竞争。我们相信这一过程也是许多文献所报道的在InGaN和AlGaN等氮化物中经常观测到的发光峰位随温度“S”形变化的主要根源。     

Growth and optical characteristics of ZnCdSe/ZnSe QWs on Si substrate with ZnO buffer

In this paper, the growth and characteristics of ZnCdSe/ZnSe quantum wells (QWs) prepared on ZnO-Si (111) templates are reported. An oriented ZnO thin film with a smooth surface was employed to be the buffer layer for the ZnCdSe/ZnSe QWs growth. Scanning electron microscopy (SEM) patterns showed that the ZnO buffer layer improved the smoothness of the ZnCdSe/ZnSe sample. Up to the 3rd longitudinal optical phonon of Zn0.56Cd0.44Se observed in Raman spectra suggests that the crystal quality of ZnCdSe/ZnSe QWs is reasonably good. The influence of quantum confinement effect on exciton characters of the QWs was also demonstrated.     

Modeling and simulation of experimentally fabricated QDSSC using ZnS as light absorbing and blocking layer

Abstract—Two main factors which limit the power conversion efficiency of solar cells are light absorption and recombination processes. In photovoltaic (PV) devices, low energy photons cannot be absorbed and excite electrons from valance band to conduction band, hence do not contribute to the current. On the other hand, high energy photons cannot be efficiently used due to a poor match to the energy gap. Existence of charge recombination in PV devices causes the low conversion performance, which is indicated by the low open-circuit voltage (V _OC ). Using a blocking layer in system could effectively reduce the recombination of charge carriers. In this study, we simulated a solar cell with ITO/ZnO/P3HT&PCBM/Ag structure. To prevent the charge recombination, a ZnS QD layer was used which acts as a light absorbing and a recombination blocking layer in the ITO/ZnO film/ZnS QD/P3HT&PCBM/Ag structure. The simulated J–V characteristics of solar cells showed a close match with the experimental results. Simulate data showed an increase of conversion efficiency in ZnS QDSSC from 1.71 to 3.10%, which is relatively 81.28% increase.     

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.     

Effects of carrier barrier on voltage controllable color tunable OLEDs

The effects of the carrier blocking layer on the emission color of the color tunable organic light emitting devices (OLEDs) have been investigated. Color tuning is controlled by the applied voltage. Both the experimental and theoretical results show that inserting a hole blocking layer between two adjacent emission layers will make the color tunable region move toward the wide bandgap emission layer of blue color in our case. By replacing the hole blocking layer with an electron blocking layer, the color tunable region will shift toward the small bandgap emission layer of red. Besides shifting the tunable region toward the pure spectral color, the introduction of the carrier blocking layer can extend the color tunable range. PACS 78.20.Bh; 78.45.+h; 78.55.Kz; 78.60.Fi; 81.05.Lg; 85.60.Jb     

利用倒双阶渐变阶梯形电子阻挡层减少深紫外激光二极管的电子泄露

本文提出了用双阶渐变阶梯和倒双阶渐变阶梯形电子阻挡层(EBL)以减少AlGaN基深紫外激光二极管(DUV-LDs)在p型区的电子泄露,并用Crosslight软件模拟仿真了双阶渐变阶梯和倒双阶渐变阶梯形EBL结构的光电特性,结果发现：具有倒双阶渐变阶梯形EBL的激光器拥有比双阶渐变阶梯形EBL激光器更高的斜率效率(SE),更高的输出功率,更低的阈值电流和阈值电压,更高的有效势垒高度和更低的电子泄露.这意味着前者拥有更强的抑制电子泄露的能力.在与矩形EBL结构对比中发现,所提出的结构还提高了有源区载流子浓度和辐射复合速率,进一步提高了DUV-LDs的光电性能.     

Influence of Blocking Interlayer in Blue Organic Light-Emitting Diodes with Different Thicknesses of Emitting Layer and Interlayer

A series of blue organic light-emitting diodes with electron or hole blocking interlayer are fabricated.Different structures of blocking interlayers can influence the position of the recombination zone due to the fact that they confine carriers in different ways.We find that the double hole blocking interlayer structure can balance carrier injection more effectively.Its power and current efficiency are more stable and the current efficiency value is30.2cd/A at 1000cd/m2.Decreasing the thicknesses of the emitting layer and interlayers is in favor of the power efficiency.The performance of the device is also affected by changing the interlayer position when we use hole and electron blocking material as interlayers simultaneously.     

电极表面改性对染料敏化太阳电池性能影响的机理研究

采用强度调制光电流谱(IMPS)和强度调制光电压谱(IMVS)技术,从染料敏化太阳电池(DSC)电子传输和复合角度对比了不同光强下导电玻璃表面阻挡层及TiO₂薄膜优化使电池性能改善的内在原因.阻挡层的引入和TiO₂薄膜的优化均通过电沉积法实现.结果表明,对多孔薄膜电极的不同改性均提高了电池的短路电流J_sc和效率η,但对电子传输和复合过程的作用机理有所不同:前者延长了电子寿命τ _n,但电子传输时间τ _d变化不明显;而后者则主要是延长τ _n的同时也缩短了τ _d. 关键词： 染料敏化 太阳电池 调制光电流谱/调制光电压谱 电子输运     

Modeling and simulation of efficiency droop in GaN-based blue light-emitting diodes incorporating the effect of reduced active volume of InGaN quantum wells

The efficiency droop of InGaN-based blue light-emitting diodes (LEDs) is analyzed using numerical simulations with a modified ABC carrier recombination model. The ABC model is modified to include the effect of reduced effective active volume of InGaN quantum wells (QWs) and incorporated into the numerical simulation program. It is found that the droop of internal quantum efficiency (IQE) can be well explained by the effect of reduced light-emitting active volume without assuming a large Auger recombination coefficient. A simulated IQE curve with the modified ABC model is found to fit quite well with a measured efficiency curve of an InGaN LED sample when the effective active volume takes only 2.5% of the physical volume of QWs. The proposed numerical simulation model incorporating the reduced effective active volume can be advantageous for use in the modeling and simulation of InGaN LEDs for higher efficiency.     

Enhancement of efficiency of multilayer polymer light-emitting diodes by inserting blocking layers

In this study, the electroluminescence efficiency of the blue-green polymer light-emitting diodes (PLEDs) is enhanced by the insertion of blocking layers. PLEDs are multilayered structures prepared with spin-coating and thermal evaporation. Blue host is doped with green guest to form a single emission layer. Poly(9-vinylcarbazole) (PVK) and 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) are used as materials for the blocking layers. The optimal thicknesses of the PVK and BCP layers are 10 and 0.2 nm, respectively. PVK plays an important role of blocking holes and electrons, and BCP not only confines holes in the emission layer but also enhances the injection of electrons from Alq₃ to the emission layer. The efficiency of a PLED with a dual-blocking layer is 2.37 times higher than that of a PLED without a blocking layer prepared because of the improved carrier balance and the enhanced carrier recombination.