一种新型全方位反射AlGaInP薄膜发光二极管

提出了一种新型全方位反射A1GalnP LED结构和制作工艺.GaAs外延片与含导电孔的SiO2,Au形成全方位反射镜后,银浆键合在Si支架上,去除GaAs衬底,制作薄AuGeNi电极,粗化,生长ITO,制作厚AuGeNi电极,合金则形成ODR薄膜LED结构.300μm×300μm管芯裸装在TO-18金属管座上,在20mA的电流驱动下,测得电压为2.2V,光强达到195mcd,光功率达到3.78mW,比常规吸收衬底LED提高3.6倍.     

全反射镜结构对AlGaInP发光二极管发光效率的影响

采用计算机模拟的方法,计算了SiO2/Al,ITO/Al,SiO2/Au和ITO/Au全方位反射镜结构和分布式布拉格反射镜的反射特性.用PECVD和溅射设备制作了Glass/SiO2/Au结构,用LP-MOCVD生长了DBR结构,并测量了其反射特性,实验与模拟结果基本吻合.从模拟和实验的结果得到,SiO2/Au ODR结构在波长为630nm的垂直入射光下反射率很高,达到91%以上.对于不同角度的入射光,SiO2/Au在20°～85°都有很高的反射率,远高于DBR结构的反射率.在实际器件测试中,ODR结构的AlGaInP红光LED比无DBR结构的LED提高了115%,比DBR结构的LED提高了28%.这说明,ODR结构与DBR结构相比可以大幅提高红光LED的出光效率.     

一种新型全方位反射AlGaInP薄膜发光二极管

提出了一种新型全方位反射A1GalnP LED结构和制作工艺.GaAs外延片与含导电孔的SiO2,Au形成全方位反射镜后,银浆键合在Si支架上,去除GaAs衬底,制作薄AuGeNi电极,粗化,生长ITO,制作厚AuGeNi电极,合金则形成ODR薄膜LED结构.300μm×300μm管芯裸装在TO-18金属管座上,在20mA的电流驱动下,测得电压为2.2V,光强达到195mcd,光功率达到3.78mW,比常规吸收衬底LED提高3.6倍.     

全反射镜结构对AlGaInP发光二极管发光效率的影响

采用计算机模拟的方法,计算了SiO2/Al,ITO/Al,SiO2/Au和ITO/Au全方位反射镜结构和分布式布拉格反射镜的反射特性.用PECVD和溅射设备制作了Glass/SiO2/Au结构,用LP-MOCVD生长了DBR结构,并测量了其反射特性,实验与模拟结果基本吻合.从模拟和实验的结果得到,SiO2/Au ODR结构在波长为630nm的垂直入射光下反射率很高,达到91%以上.对于不同角度的入射光,SiO2/Au在20°～85°都有很高的反射率,远高于DBR结构的反射率.在实际器件测试中,ODR结构的AlGaInP红光LED比无DBR结构的LED提高了115%,比DBR结构的LED提高了28%.这说明,ODR结构与DBR结构相比可以大幅提高红光LED的出光效率.     

Luminance Enhancement of Flip-Chip Light-Emitting Diodes by Geometric Sapphire Shaping Structure

The flip-chip light-emitting diodes (FC-LEDs) with geometric sapphire shaping structure were investigated. The sapphire shaping structure was formed on the bottom side of the sapphire substrate by a chemical wet etching technique for light extraction purpose. The crystallography-etched facets were (1010) M-plane, (1102) R-plane, and (1120) A-plane against the (0001) c-axis with the angles range between 29deg~60deg. These large slope oblique sidewalls are useful for light extraction efficiency enhancement. The light-output power of sapphire shaping FC-LEDs was increased 55% (at 350-mA current injection) compared to that of conventional FC-LEDs.     

Thermal Study of High-Power Nitride-Based Flip-Chip Light-Emitting Diodes

This paper presents a chip-level thermal study of high-power nitride-based flip-chip (FC) light-emitting diodes (LEDs). In order to understand the thermal performance of the high-power FC LEDs thoroughly, a quantitative parametric analysis of the thermal dependence on the chip contact area, bump configuration, and bump defects was performed by finite-elementmodel (FEM) numerical simulation and thermal infrared (IR) microscopy testing, respectively. FEM numerical simulation results proved that the optimized bump configuration design was essential to get a uniform temperature distribution in the active layer and improve the thermal performance of the FC LED. IR microscopy testing results recognized that bump defects formed in the LED chip solder processing would lead to surface hot spots around the vicinity of these bump defects, particularly under high-current working conditions. In addition, a light-emitting dark zone was also observed in the optical field for FC LEDs with bump defects. In summary, optimized LED FC bump configuration design and good bonding quality in the chip bonding process are proved to be critical for improving the thermal performance and extending the operating longevity of high-power FC LEDs.      

基于LED应用的分布布拉格反射器研究进展

从材料体系、结构设计和降低串电阻方法等方面系统阐述了分布布拉格反射器（DBR）在发光二极管（LED）器件中的发展情况,并对分布DBR的发展提出了几点研究意见。     

垂直结构LED和倒装结构LED的发光特性研究

研究了1.16 mm GaN基蓝光芯片的垂直封装结构LED和倒装封装结构LED在驱动电流达到和超过工作电流350mA的发光特性和变化趋势.随着驱动电流的逐渐增大,与垂直结构LED相比,倒装结构LED光通量的饱和电流值增加350mA,在1 200 mA电流时的光通量高出25.9％,色温的异常电流值增加了400 mA,发光效率平均提高81 m/W.实验结果表明,倒装结构LED具有更高的抗大电流冲击稳定性和光输出性能,可有效提高LED在实际应用中使用寿命.     

Improved Light Extraction of Nitride-Based Flip-Chip Light-Emitting Diodes Via Sapphire Shaping and Texturing

A novel flip-chip structure of GaN-sapphire light-emitting diodes (LEDs) was developed to improve the external quantum efficiency, where the sapphire substrate was textured and shaped with beveled sidewalls using a wet etching technique. The forward voltage of the conventional flip-chip and shaped flip-chip GaN LEDs were 2.84 and 2.85 V at 20 mA, respectively. This indicates that the GaN LED was not destroyed during the sapphire wet etching process. It was found that the output power increased from 9.3 to 14.2 mW, corresponding to about 52% increases in the external quantum efficiency. The results agree well with the simulation data that the shaped flip-chip GaN LED can provide better light extraction efficiency than that of the conventional flip-chip sample     

Electrostatic Reliability Characteristics of GaN Flip-Chip Power Light-Emitting Diodes With Metal–Oxide–Silicon Submount

The electrostatic reliability characteristics of gallium nitride flip-chip (FC) power light-emitting diodes (PLEDs) with metal-oxide-silicon (MOS) submount are investigated for the first time. The electrostatic damage reliability of the reported diode submount and that of our proposed simple structure MOS submount are fabricated and compared. Their corresponding electrostatic protection capabilities are increased from 200 V (conventional PLED) to 500 V (FC-PLED on diode submount), to 500 V (FC-PLED on MOS submount with a SiO₂ thickness of 297 A?), and even to a value as high as 1000 V (FC-PLED at a SiO₂ thickness of 167 A?), which are much higher than the PLED industrial test value of 150 V at -5 V/-10 ? A criterion and are also much more robust than the previous academic reports.     

Efficiency Enhancement and Beam Shaping of GaN–InGaN Vertical-Injection Light-Emitting Diodes via High-Aspect-Ratio Nanorod Arrays

The enhanced light extraction and collimated output beam profile from GaN–InGaN vertical-injection light-emitting diodes (VI-LEDs) are demonstrated utilizing high-aspect-ratio nanorod arrays. The nanorod arrays are patterned by self-assembled silica spheres, followed by inductively coupled-plasma reactive ion etching. The fabricated nanorod arrays not only provide an omnidirectional escaping zone for photons, but also serve as waveguiding channels for the emitted light, resulting in a relatively collimated beam profile. The light output power of the VI-LED with nanorod arrays is enhanced by 40%, compared to a conventional VI-LED. The measured far-field profiles indicate that the enhancement is mainly along the surface normal direction, within a view angle of 20 $^{circ}$.      

InGaN-Based Light-Emitting Diodes With Nanoporous Microhole Structures

InGaN-based light-emitting diodes (LEDs) with nanoporous microhole array (NMA) structures were fabricated through photoelectrochemical wet oxidation and oxide-removing processes. The average size of the nanoporous structure at the microhole regions was measured at 60-80 nm. Forward voltages were measured at 3.47 and 3.68 V for a standard LED (ST-LED) and an NMA-LED, respectively, the latter caused by the higher contact resistance at the nanoporous GaN:Mg surface. The light output power of the NMA-LED had a 40.5% enhancement compared with the ST-LED on nonencapsulated LEDs in chip form. The higher light scattering process occurred at the NMA structure on the GaN:Mg surface and at the ringlike patterns on the GaN:Si structure. The results were a higher light extraction efficiency and a larger divergent angle in the NMA-LED.     

Improvement of Light Extraction From Patterned Polymer Encapsulated GaN-Based Flip-Chip Light-Emitting Diodes by Imprinting

To improve surface light extraction of GaN-based flip-chip light-emitting diodes (FC-LEDs), we employed an imprint approach of thermosetting polymer for patterning microscale surface grating on the polymer encapsulant. One-dimensional (1-D) and two-dimensional (2-D) taper-like polymer gratings with a period of 6 mum were successfully realized on encapsulant above the sapphire backplane of GaN LED. By adopting the 1-D and 2-D taper-like grating encapsulant, the improvement of light extraction from the 1 mm times 1 mm FC-blue LED with a reflective Ag film on the p-side was about 18.5% and 31.9% compared to the LED encapsulated by flat polymer, respectively. To evaluate the concept of a diffraction grating in enhancement of light extraction, we performed a simulation of diffraction based on 1-D rigorous coupled wave analysis with the supporting experiments.     

Nitride-Based Thin-Film Light-Emitting Diodes With Photonic Quasi-Crystal Surface

In this letter, the nitride-based thin-film light-emitting diodes (TFLEDs) with eight-fold photonic quasi-crystal (PQC) surfaces are proposed and demonstrated by a combination of wafer bonding, laser lift-off, and electron-beam lithography processes. By adopting a PQC surface, the light–output power (at 350 mA) of the PQC-TFLEDs exhibits 140% output power enhancement as compared with that of TFLEDs without a PQC surface.      

Enhanced Light Extraction in Wafer-Bonded AlGaInP-Based Light-Emitting Diodes via Micro- and Nanoscale Surface Textured

AlGaInP-based metal-bonding light-emitting diodes (LEDs) with micro- and nanoscale textured surface were investigated. The device surface with microbowls and nanorods were formed by a chemical wet-etching and dry-etching technique for enhancing light-extraction purpose. The luminous intensity could be enhanced 65.8% under 20-mA current injection as compared with the plane surface LEDs. The maximum wall-plug efficiency was achieved 14.1% at 7.5-mA operation.     

Enhancement of Light Extraction Efficiency Using Lozenge-Shaped GaN-Based Light-Emitting Diodes

We have demonstrated both theoretically and experimentally that a lozenge-shaped light-emitting diode (LED) enhances light extraction efficiency compared with a conventional rectangular LED. The total light output power of the lozenge-shaped LED on a transmitter optical can (TO-can)-type package shows an increase of 12% at an injection current of 20 mA when compared with that of a rectangular LED. Moreover, the series resistance and the forward voltage of the lozenge-shaped LED slightly decrease compared with those of the rectangular LED. The far-field emission pattern shows that the light escaping from the lozenge-shaped LED along the horizontal direction is larger than that from the rectangular LED.      

Enhancement of Light Extraction Efficiency of Gallium Nitride Flip-Chip Light-Emitting Diode With Silicon Oxide Hemispherical Microlens on its Back

Silicon oxide (SiO₂) hemispherical microlens with the density of 8.2 times 10⁸ cm^-2 has been formed on a sapphire substrate of gallium nitride (GaN) light-emitting diode (LED) by liquid phase deposition to enhance the light extraction efficiency. For flip-chip LED, the SiO₂ microlens exhibits 1.25 times enhancement of optical output power. In comparison of the conventional LED, there is 61% enhancement for flip-chip LED with a SiO₂ microlens.     

Linear Cascade Arrays of GaN-Based Green Light-Emitting Diodes for High-Speed and High-Power Performance

In the following study, we demonstrated linear cascade GaN-based light-emitting-diode (LED) arrays at a wavelength of approximately 520 nm. Experimental LEDs were analyzed with the goal to improve the output power and differential efficiency of a single LED. The study shows that using arrays with up to four LEDs connected in series, we can achieve four times the improvement in output power (differential quantum efficiency) under the same bias current as compared to a single LED apparatus. We have also measured the modulation-speed performance of experimental LEDs, and both devices exhibit similar 3-dB bandwidth (90 MHz) under the same bias currents. Experimental results indicate that the cascade connection offers the advantages of significantly enhanced external differential efficiency and provision of a method to use a constant-voltage power supply. The current crowding problem and resistance-capacitance-limited bandwidth degradation issues in a large active area LED can also be minimized using the connection demonstrated in our experiment.