基于InGaN/GaN多量子阱双波长发光二极管生长及发光性能

对基于InGaN/GaN量子阱的蓝绿双波长发光二极管的材料生长和发光性质进行了研究.通过设计生长多组具有不同参量的外延结构,获得了优化的双波长量子阱结构参量,指出量子阱位置的分布、蓝绿阱间垒的宽度以及材料构成对量子阱发光性能均有较大影响.对双波长发光二极管器件光学性质进行了研究,结果表明,InGaN/GaN量子阱发光更依赖于In团簇形成的局域激子发光,从而导致了小电流下的反常光学现象.通过数值计算材料内部极化场的强度,对波长漂移的原因进行了解释,并通过双波长发光效率拟合分析了发光二极管"droop"效应可能的产生机理.

Reduction of Efficiency Droop and Modification of Polarization Fields of InGaN-Based Green Light-Emitting Diodes via Mg-Doping in the Barriers

We demonstrate that the Mg-doping in barriers can partially screen the polarization fields of InGaN-based green light-emitting diodes.The photocurrent spectra show that the Mg-doping samples have smaller polarization fields and the blue shift of the peak with increasing current is observed.The reduction of polarization fields can be attributed to the screening of the impurity holes generated by the Mg atoms in the barriers.The efficiency droop is sensitive to the Mg-doping concentration in barriers,while the sample with Mg concentration of 5×10^(19) cm^(-3) exhibits the lowest efficiency degradation of 12.4%at a high injection current.

AlGaInP红、橙、黄光高亮度LED外延材料

采用金属有机化合物汽相淀积技术生长用于高亮度发光管 (UB-L ED)的 Al Ga In P/Ga As半导体微结构材料 ,突破了材料结构设计和材料生长工艺的关键技术 ,生长出满足于 Cd级的红、橙、黄光 L ED器件的外延材料。

Influence of growth conditions on the V-defects in InGaN/GaN MQWs

The influence of the growth temperature,TMIn/TEGa andⅤ/Ⅲratio on the V-defects of InGaN/GaN multi-quantum wells（MQWs） has been investigated and discussed.When the TMIn flow increases from 180 to 200 sccm,the density of V-defects increases from 2.72×10^（18） to 5.24×10^（18） cm^（-2）,and the V-defect width and depth increase too.The density also increases with the growth temperature.The densities are 2.05×10~8,2.72×10^（18） and 4.23×10~8 cm^（-2）,corresponding to a growth temperature of 748,753 and 758℃respectively.When the NH_3 flows are 5000,6600 and 8000 sccm,the densities of the V-defects of these samples are 6.34×10^（18）,2.72×10^（18） and 4.13×10^（18） cm^（-2）,respectively.A properⅤ/Ⅲratio is needed to achieve step flow growth mode.We get the best quality of InGaN/GaN MQWs at a growth temperature of 753℃TMIn flow at 180 sccm,NH_3 flow at 6600 sccm,a flatter surface and less V-defects density.The depths of these V-defects are from 10 to 30 nm,and the widths are from 100 to 200 nm.In order to suppress the influence of V-defects on reverse current and electro-static discharge of LEDs,it is essential to grow thicker p-GaN to fill the V-defects.

AlGaN/GaN high electron mobility transistors with selective area grown p-GaN gates

We report a selective area growth（SAG） method to define the p-GaN gate of AlGaN/GaN high electron mobility transistors（HEMTs） by metal-organic chemical vapor deposition.Compared with Schottky gate HEMTs,the SAG p-GaN gate HEMTs show more positive threshold voltage（Vth） and better gate control ability.The influence of Cp2Mg flux of SAG p-GaN gate on the AlGaN/GaN HEMTs has also been studied.With the increasing Cp2Mg from 0.16 μmol/min to 0.20 μmol/min,the Vth raises from-0.67 V to-0.37 V.The maximum transconductance of the SAG HEMT at a drain voltage of 10 V is 113.9 mS/mm while that value of the Schottky HEMT is 51.6 mS/mm.The SAG method paves a promising way for achieving p-GaN gate normally-off AlGaN/GaN HEMTs without dry etching damage.

Improvement of the efficiency droop of GaN-LEDs using an AlGaN/GaN superlattice insertion layer

With an n-A1GaN （4 nm）/GaN （4 nm） superlattice （SL） inserted between an n-GaN and an InGaN/GaN multiquantum well active layer, the efficiency droop of GaN-based LEDs has been improved. When the injection current is lower than 100 mA, the lumen efficiency of the LED with an n-AlGaN/GaN SL is relatively small compared to that without an n-AlGaN/GaN SL. However, as the injection current increases more than 100 mA, the lumen efficiency of the LED with an n-A1GaN/GaN SL surpasses that of an LED without an n-AlGaN/GaN SL. The wall plug efficiency of an LED has the same trend as lumen efficiency. The improvement of the efficiency droop of LEDs with n-AIGaN/GaN SLs can be attributed to a decrease in electron leakage due to the enhanced current spreading ability and electron blocking effect at high current densities. The reverse current of LEDs at -5 V reverse voltage decreases from 0.2568029 to 0.0070543 μA, and the electro-static discharge （ESD） pass yield of an LED at human body mode （HBM）-ESD impulses of 2000 V increases from 60% to 90%.

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

The advantages of the p-AIInGaN/GaN superlattices＇ （SLs） structure as an electron blocking layer （EBL） for InGaN blue light-emitting diodes （LEDs） were studied by experiment and APSYS simulation. Elec- troluminescence （EL） measurement results show that the LEDs with the p-AllnGaN/GaN SLs＇ structure EBL ex- hibited better optical performance compared with the conventional A1GaN 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.

Evaluation of light extraction efficiency for the light-emitting diodes based on the transfer matrix formalism and ray-tracing method

The internal quantum efficiency（IQE） of the light-emitting diodes can be calculated by the ratio of the external quantum efficiency（EQE） and the light extraction efficiency（LEE）.The EQE can be measured experimentally,but the LEE is difficult to calculate due to the complicated LED structures.In this work,a model was established to calculate the LEE by combining the transfer matrix formalism and an in-plane ray tracing method.With the calculated LEE,the IQE was determined and made a good agreement with that obtained by the ABC model and temperature-dependent photoluminescence method.The proposed method makes the determination of the IQE more practical and conventional.