Influence of Si-doping on the characteristics of InGaN-GaN multiplequantum-well blue light emitting diodes

A detailed study on the effects of Si-doping in the GaN barrier layers of InGaN-GaN multiquantum well (MQW) light-emitting diodes (LEDs) has been performed. Compared with unintentionally doped samples, X-ray diffraction results indicate that Si-doping in barrier layers can improve the crystal and interfacial qualities of the InGaN-GaN MQW LEDs. It was also found that the forward voltage is 3.5 and 4.52 V, the 20-mA luminous intensity is 36.1 and 25.1 mcd for LEDs with a Si-doped barrier and an unintentionally doped barrier, respectively. These results suggests that one can significantly improve the performance of InGaN-GaN MQW LEDs by introducing Si doping in the GaN barrier layers     

InGaN-AlInGaN multiquantum-well LEDs

InGaN-GaN and InGaN-AlInGaN multiquantum-well (MQW) light-emitting diodes (LEDs) were both fabricated and their optical properties were evaluated by photoluminescence (PL) as well as electroluminescence (EL). We found that the PL peak position of the InGaN-AlInGaN MQW occurs at a much lower wavelength than that of the InGaN-GaN MQW. The PL intensity of the InGaN-AlInGaN MQW was also found to be larger. The EL intensity of the InGaN-AlInGaN MQW LED was also found to be larger than that of the InGaN-GaN MQW LED under the same amount of injection current. Furthermore, it was found that EL spectrum of the InGaN-AlInGaN MQW LED is less sensitive to the injection current. These observations all suggest that we can improve the properties of nitride-based LEDs by using AlInGaN as the barrier layer     

AlGaN/GaN层叠结构插入层改善氮化镓基发光二极管抗静电性能研究

在GaN基发光二极管的uGaN与nGaN之间插入AlGaN/GaN层叠结构,增大了外延层的张应力,降低了外延层中的穿透位错密度,改善了外延材料的质量。对比了AlGaN/GaN层叠结构中不同Al组分对LED的抗静电能力的影响,含6.8%铝组分AlGaN/GaN层叠结构的LED人体模式抗静电能力提高到了6000V,合格率超过了95%。     

Improved III-nitrides based light-emitting diodes anti-electrostatic discharge capacity with an AlGaN/GaN stack insert layer

Through insertion of an AlGaN/GaN stack between the u-GaN and n-GaN of GaN-based light-emitting diodes(LEDs),the strain in the epilayer was increased,the dislocation density was reduced.GaN-based LEDs with different Al compositions were compared.6.8%Al composition in the stacks showed the highest electrostatic discharge(ESD) endurance ability at the human body mode up to 6000 V and the pass yield exceeded 95%.     

Improved ⅢI-nitrides based light-emitting diodes anti-electrostatic discharge capacity with an AlGaN/GaN stack insert layer

Through insertion of an AlGaN/GaN stack between the u-GaN and n-GaN of GaN-based light-emitting diodes (LEDs),the strain in the epilayer was increased,the dislocation density was reduced.GaN-based LEDs with different Al compositions were compared.6.8％ A1 composition in the stacks showed the highest electrostatic discharge (ESD) endurance ability at the human body mode up to 6000 V and the pass yield exceeded 95％.     

Enhanced output power in an InGaN-GaN multiquantum-welllight-emitting diode with an InGaN current-spreading layer

InGaN-GaN multiple quantum-well (MQW) light-emitting diodes (LEDs) with InGaN current-spreading layer were grown by metal-organic vapor-phase epitaxy (MOVPE) and their characteristics were evaluated by current-voltage (I-V), as well as output power measurements. Experimental results indicate that the LEDs exhibited a higher output power and a lower operation voltage than that of conventional LEDs. The external quantum efficiency of InGaN-GaN MQW LEDs for bare chips operated at injection current of 20 mA with InGaN current spreading layer near 5%. This is two times higher than that of conventional LEDs. This could be tentatively attributed to the better current-spreading effect resulting from Si-doped In_0.18Ga_0.82N wide potential well in which electron states are not quantized     

Improvement of near-ultraviolet InGaN-GaN light-emitting diodes with an AlGaN electron-blocking layer grown at low temperature

The 400-nm near-ultraviolet InGaN-GaN multiple quantum well light-emitting diodes (LEDs) with Mg-doped AlGaN electron-blocking (EB) layers of various configurations and grown under various conditions, were grown on sapphire substrates by metal-organic vapor phase epitaxy system. LEDs with AlGaN EB layers grown at low temperature (LT) were found more effectively to prevent electron overflow than conventional LEDs with an AlGaN one grown at high temperature (HT). The electroluminescent intensity of LEDs with an LT-grown AlGaN layer was nearly three times greater than that of LEDs with an HT-grown AlGaN. Additionally, the LEDs with an LT-grown AlGaN layer in H/sub 2/ ambient were found to increase the leakage current by three orders of magnitude and reduce the efficiency of emission.     

Nitride-based green light-emitting diodes with high temperature GaN barrier layers

High-quality InGaN-GaN multiquantum well (MQW) light-emitting diode (LED) structures were prepared by temperature ramping method during metalorganic chemical vapor deposition (MOCVD) growth. It was found that we could reduce the 20-mA forward voltage and increase the output intensity of the nitride-based green LEDs by increasing the growth temperature of GaN barrier layers from 700/spl deg/C to 950/spl deg/C. The 20-mA output power and maximum output power of the nitride-based green LEDs with high temperature GaN barrier layers was found to be 2.2 and 8.9 mW, respectively, which were more than 65% larger than those observed from conventional InGaN-GaN green LEDs. Such an observation could be attributed to the improved crystal quality of GaN barrier layers. The reliability of these LEDs was also found to be reasonably good.     

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.     

White-light emission from InGaN-GaN multiquantum-welllight-emitting diodes with Si and Zn codoped active well layer

Si and Zn codoped In_xGa_1-xN-GaN multiple-quantum-well (MQW) light-emitting diode (LED) structures were grown by metal-organic vapor phase epitaxy (MOVPE). It was found that we can observe a broad long-wavelength donor-acceptor (D-A) pair related emission at 500 nm~560 nm. White light can thus be achieved by the combination of such a long-wavelength D-A pair emission with the InGaN bandedge related blue emission. It was also found that the electroluminescence (EL) spectra of such Si and Zn codoped InGaN-GaN MQW LEDs are very similar to those measured from phosphor-converted white LEDs. That is, we can achieve white light emission without the use of phosphor by properly adjusting the indium composition and the concentrations of the codoped Si and Zn atoms in the active well layers and the amount of injection current     

High efficiency and improved ESD characteristics of GaN-based LEDs with naturally textured surface grown by MOCVD

The following paper presents a study on GaN-based light-emitting diodes (LEDs) with naturally textured surface grown by metal-organic chemical vapor deposition. The study utilizes a well-known approach of increasing light extraction efficiency. The approach is based on naturally formed V-shaped pits on surface that originate from low-temperature-growth (LTG) conditions of topmost p-GaN contact layer. In our experiment, the high-temperature-grown (HTG) p-GaN layer was inserted between the p-AlGaN electron-blocking layer and the LTG p-GaN contact layer, in order to suppress pit-related threading dislocations (TDs). These TDs may intersect the underlying active layer. The results of the experiment show that GaN-based LEDs with the HTG p-GaN insertion layer can effectively endure negative electrostatic discharge voltage of up to 7000 V. We also noted that application of 20-mA current injection yields output power of about 16 mW for the LEDs emitting around 465 nm. The output power results correspond to an external quantum efficiency of around 30%.     

p-AlGaN/GaN超晶格做p型层350 nm紫外AlGaN基LED

使用p-AlGaN/p-GaN SPSLs作为LED的p型层,在蓝宝石衬底上生长出发光波长为350 nm的AlGaN基紫外LED。[JP+1]由于AlGaN/GaN超晶格的极化效应,使得Mg受主的电离能降低,大幅提高了器件的光学和电学性能。在工作电流为350 mA下发光亮度达到了22.66 mW,相应的工作电压为3.75 V,LEDs的光功率满足了实际应用需求。     

Nitride-Based Near-Ultraviolet Mesh MQW Light-Emitting Diodes

We have demonstrated nitride-based near-ultraviolet mesh multiquantum-well (MQW) light-emitting diodes (LEDs) by etching through the MQW active region. With 20-mA injection current, it was found that forward voltages were 3.29, 3.31, and 3.38 V while output powers were 7.5, 9.0, and 11.3 mW for the planar indium-tin-oxide (ITO) LED, mesh ITO LED, and mesh MQW LED, respectively. The larger LED output power is attributed to the increased light extraction efficiency.     

低温生长n型氮化镓插入层提高LED抗静电能力

在这篇论文里,我们通过在InGaN/GaN 多量子阱和n型氮化镓层中间插入一层低温生长的n型氮化镓显著提高了LED的抗静电能力。通过引入低温生长的氮化镓插入层使得LED抗击穿电压超过4000V的良品率从9.9%提升到74.7%。低温生长的氮化镓插入层作为后续生长的多量子阱的缓冲层,释放了量子阱中的应力并且改善了量子阱的界面质量。另外,我们证明了在氮气气氛下生长低温氮化镓插入层对于LED抗静电能力的改善要强于氢气气氛,同时也进一步证明低温插入层对量子阱中应力的释放有利于提高LED的抗静电能力。光电测试结果表明,在引入低温nGaN缓冲层后,LED的电学特性并没有衰退,并且LED的光输出功率提高了13.9%。     

Experimental study of GaN based blue light emitting diodes with a thin AlInN layer in front of the electron blocking layer

The GaN based blue light emitting diodes (LEDs) with a thin AlInN layer inserted in front of the electron blocking layer (EBL) are experimentally studied. It is found that inserting a thin EBL can improve the light output power and reduce the efficiency droop compared with the conventional AlGaN counterparts. Based on numerical simulation and analysis, the improvement on the electrical and optical characteristics is mainly attributed to the reduction of the electron leakage current, which increases the concentration of carriers in the quantum well (QW) when the thin AlInN layer is used.     

钝化材料对深紫外LED器件性能的影响

对比研究了SiO2、聚酰亚胺薄膜、SiNx/旋涂玻璃(SOG)复合材料等钝化材料对倒装焊深紫外LED器件抑制漏电流恶化、改善器件可靠性的作用。实际测试结果表明,未钝化和采用SiO2、聚酰亚胺、SiNx/SOG复合钝化膜后,倒装焊紫外LED短路漏电比例分别为100%、100%、55%和18%,采用聚酰亚胺和SiNx/SOG复合钝化膜的器件点亮1 000h后光衰分别为67%和20%。分析表明,SiNx与SOG结合使用有效降低了表面电荷复合几率并改善了倒装焊短路问题;SOG还进一步降低了表面的粗糙度,改善了由于AlGaN外延表面上的深凹槽结构引起的器件漏电及倒装焊金属溢流的短路,从而大大提高了可靠性。     

Gradient Doping of Mg in p-Type GaN for High Efficiency InGaN–GaN Ultraviolet Light-Emitting Diode

The performance of a InGaN-GaN multiple quantum-well (MQW) ultraviolet (UV) light-emitting diode (LED) with an emission of 385 nm was enhanced by a gradient doping of Mg in the p-GaN layer. The optical output power was enhanced by 21% at an input current of 20 mA compared to that of a UV LED with a uniformly doped p-GaN layer. The improved performance of the UV LED could be attributed to the decrease in diffusion of Mg into MQW and the suppression of electron transport from the conduction band of the MQW to the acceptor level of the deep donor acceptor pair bands in the p-GaN layer by a gradient doping of Mg in p-GaN layer.     

Improvement of near-ultraviolet InGaN-GaN light-emitting diodes through higher pressure grown underlying GaN layers

The 410-nm near-ultraviolet (near-UV) InGaN-GaN multiple quantum-wells light-emitting diodes (LEDs) with low-pressure-grown (200 mbar) and high-pressure-grown (400 mbar) Si-doped GaN underlying layers were grown on c-face sapphire substrates by metal-organic vapor phase epitaxy. Increasing the growth pressure during the initial growth of the underlying n-type GaN epilayers of the near-UV InGaN-GaN LEDs was found to reduce the amount of threading dislocations that originated from the GaN-sapphire interfaces. The electroluminescence intensity of LEDs with underlying GaN layers grown at a higher pressure was nearly five times larger than that of LED with layers grown at lower pressure. Additionally, two-order reduction of leakage current was also induced for the LEDs grown at a higher pressure.     

p-GaN-i-GaN/AlGaN multiple-quantum well n-AlGaN back-illuminated ultraviolet detectors

The spectral response of back-surface-illuminated p-GaN-i-GaN/AlGaN multiplequantum well (MQW)-n-AlGaN ultraviolet (UV) photodetector is reported. The structure was grown by molecular-beam epitaxy on a c-plane sapphire substrate. A MQW is introduced into the active region of the device to enhance the quantum efficiency caused by the high absorption coefficient of the two-dimensional (2-D) system. Another advantage of using MQW in the active region is the ability to tune the cutoff wavelength of the photodetector by adjusting the well width, well composition, and barrier height. The zero-bias peak responsivity was found to be 0.095 A/W at 330 nm, which corresponds to 36% quantum efficiency from as-grown p-i-n GaN/AlGaN MQW devices. An anomalous effect, occurring in responsivity as a negative photoresponse in the spectra peaked at 362 nm because of poor ohmic contact to p-type GaN, was also observed. Etching the sample in KOH for 30 sec before fabrication removed the surface contaminants and improved the surface smoothness of the as-grown sample, resulting in significant improvement in the device performance, giving a peak responsivity of 0.12 A/W. The device has a quantum efficiency of 45% at 330 nm without the anomalous negative photocurrent.     

Study of dual-blue light-emitting diodes with asymmetric AlGaN graded barriers

A dual-blue light-emitting diode （LED） with asymmetric A1GaN composition-graded barriers but without an AlGaN electron blocking layer （EBL） is analyzed numerically. Its spectral stability and efficiency droop are improved compared with those of the conventional InGaN/GaN quantum well （QW） dual-blue LEDs based on stacking structure of two In0.18Ga0.szN/GaN QWs and two In0.12Ga0.88N/GaN QWs on the same sapphire substrate. The improvement can be attributed to the markedly enhanced injection of holes into the dual-blue active regions and effective reduction of leakage current.