Enhancement of Flip-Chip Light-Emitting Diodes With Omni-Directional Reflector and Textured Micropillar Arrays

The flip-chip light-emitting diodes (FC-LEDs) with a conductive omni-directional reflector and textured micropillar arrays were investigated. The micropillar arrays structure was formed on the bottom side of sapphire substrate by dry etching process to increase the light-extraction efficiency. The light output power of the FC-LED was increased by 65% for a 3.2-mum textured micropillar on the bottom side of the sapphire substrate. Our work offers promising potential for enhancing output powers of commercial light-emitting devices.     

基于胶体球掩模板法制备图形化蓝宝石衬底

制备并研究了纳米级图形化蓝宝石衬底.采用磁控溅射技术在蓝宝石衬底上沉积 SiO2薄膜,利用自组装方法在SiO2薄膜上制备单层聚苯乙烯(PS)胶体球阵列,利用感应耦合等离子体干法刻蚀将周期性PS胶体球的图形转移到SiO2薄膜上,通过湿法腐蚀制备了纳米级图形化蓝宝石衬底.利用扫描电子显微镜对胶体球掩膜、SiO2纳米柱掩膜和图形化蓝宝石衬底结构进行了观察,研究了湿法腐蚀蓝宝石衬底的中间产物对刻蚀的影响,分析了腐蚀温度和腐蚀时间对蓝宝石衬底的影响.结果表明,湿法腐蚀的中间产物会降低蓝宝石衬底的刻蚀速率.蓝宝石衬底的腐蚀速率随着腐蚀温度的升高而加快;在同一腐蚀温度下,随着腐蚀时间的增加,图形尺寸进一步减小.     

对胶体球光刻中单层胶体晶体曝光特性的研究

对胶体球光刻中单层胶体晶体(MCC)的曝光特性进行了研究。利用磁控溅射的方法在蓝宝石衬底上生长SiO2薄膜并旋涂光刻胶,通过固液界面自组装的方法在光刻胶上制备了单层胶体晶体。胶体球光刻利用单层胶体晶体作为微透镜阵列,通过紫外曝光的方法在光刻胶上制备微孔阵列。光刻胶上图形的周期性与胶体球的直径有关,并且大直径的胶体球的聚光性能要强于小直径胶体球,在曝光过程中随着曝光时间的增加,由于曝光量的增加以及光刻胶的漂白现象,光刻胶上微孔的尺寸也在增加。最后以曝光后的光刻胶为掩膜,将感应耦合等离子体刻蚀技术(ICP)以及湿法腐蚀相结合,制备出了图形化蓝宝石(PSS)衬底。     

Enhancing the Light Extraction of (Alx Ga1 − x) 0.5In0.5P-Based Light-Emitting Diode Fabricated via Geometric Sapphire Shaping

AlGaInP-based light-emitting diodes (LEDs) with a transparent sapphire substrate were fabricated by the glue-bonding (GB) method. This transparent sapphire substrate is a geometric shaping structure by wet etching processes. Furthermore, the n-side-up surface has a nano-roughened texture by natural mask and chemical wet etching processes. The light output of this novel LED structure could be enhanced about 26.7% (at 350 mA) due to the higher light extraction as compared with the conventional GB-LEDs.     

Fabrication of cantilever arrays with nano-aperture hollow tips for parallel microplasma etching

For the application of parallel microplasma etching, cantilever arrays with nano-aperture hollow pyramid tips have been successfully fabricated. The SiO₂ cantilever arrays and hollow tips are formed by thermal oxidation on a Si (1 0 0) wafer with pyramid cavities. Due to the stress-dependent nonuniform oxidation, the oxide thickness is about 400 nm at the tip apexes which is much thinner than the 1.2 μm thick sidewalls. Based on these nonuniform oxide hollow tips, nano-apertures of 50-200 nm in diameter are obtained at the apexes after the following 1:10 water-diluted HF isotropic etching. The base widths of the hollow tips are designed to be 50 and 100 μm with the final sidewall thickness of only 600 nm. Consequently, the width-thickness ratio (hollow pyramid tip base width/sidewall thickness) is up to 150:1. Some improvements are made in the fabrication process and these fragile tips are obtained with a product yield of more than 90%. Then, cantilever arrays with hollow tips are released consistently and the bending behavior is discussed. In addition, preliminary experiments and simulations of microplasma generation and extraction confirm the application feasibility of this structure in parallel microplasma etching.     

GaN-based light emitting diodes on nano-hole patterned sapphire substrate prepared by three-beam laser interference lithography

Nano-hole patterned sapphire substrates (NHPSSs) were successfully prepared using a low-cost and high-efficiency approach, which is the laser interference lithography (LIL) combined with reactive ion etching (RIE) and inductively coupled plasma (ICP) techniques. Gallium nitride (GaN)-based light emitting diode (LED) structure was grown on NHPSS by metal organic chemical vapor deposition (MOCVD). Photoluminescence (PL) measurement was conducted to compare the luminescence efficiency of the GaN-based LED structure grown on NHPSS (NHPSS-LED) and that on unpatterned sapphire substrates (UPSS-LED). Electroluminescence (EL) measurement shows that the output power of NHPSS-LED is 2.3 times as high as that of UPSS-LED with an injection current of 150 mA. Both PL and EL results imply that NHPSS has an advantage in improving the crystalline quality of GaN epilayer and light extraction efficiency of LEDs at the same time.     

Improvement of light extraction efficiency of flip-chip light-emitting diode by texturing the bottom side surface of sapphire substrate

A high light-extraction efficiency was demonstrated in the flip-chip light-emitting diode (FCLED) with a textured sapphire substrate. The bottom side of a sapphire substrate was patterned using a dry etching process to increase the light-extraction efficiency. Light output power measurements indicated that the scattering of photons emitted in the active layer was considerably enhanced at the textured sapphire substrate resulting in an increase in the probability of escaping from the FCLED. The light-output power of the FCLED was increased by 40.2% for a 0.4-/spl mu/m deep FCLED with a periodic distance of 13-/spl mu/m mesh-type texture on the bottom side of the sapphire substrate.     

图形化蓝宝石衬底工艺研究进展

图形化蓝宝石衬底(PSS)技术是一种提高LED亮度的新技术。结合光刻和刻蚀工艺制作图形化蓝宝石衬底。有关图形化蓝宝石衬底的研究主要集中在对光刻和刻蚀工艺的研究,以及图形化蓝宝石衬底提高LED亮度的机理。目前微米级图形化蓝宝石衬底已经得到普遍的应用,与基于平坦蓝宝石衬底的LED相比,PSS-LED的发光功率提高了30%左右。图形化蓝宝石衬底技术的发展经历了从早期的条纹状图形到目前应用较广的半球形和锥形图形,从湿法刻蚀到干法刻蚀,从微米级到纳米级图形的演变。由于能够显著提高LED亮度,纳米级图形化蓝宝石必将得到广泛的运用。     

基于157nm深紫外激光的蓝宝石基片微加工

为了探索157nm深紫外激光对蓝宝石材料的微加工技术,采用157nm激光微加工系统,对蓝宝石基片进行了扫描刻蚀和打孔加工,以研究激光工艺参量与刻蚀深度、表面形貌的关系,分析了157nm深紫外激光对蓝宝石材料的作用机理,并利用扫描刻蚀法在蓝宝石基片上加工了一个2维图形。由实验结果可知,157nm深紫外激光作用于蓝宝石材料是一个光化学作用与光热作用并存的加工过程,适合扫描刻蚀的加工参量为能量密度3.2J/cm2,重复频率10Hz～20Hz,扫描速率0.15mm/min;在能量密度2.5J/cm2下的刻蚀率为0.039μm/pulse。结果表明,通过对激光重复频率和扫描速度的控制可实现蓝宝石材料的精细微加工。     

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.     

用原子力显微镜和扫描电镜研究GaN外延层中的位错腐蚀坑

用原子力显微镜和扫描电镜相结合的方法表征了KOH腐蚀后的Si掺杂GaN外延层中的位错腐蚀坑.根据腐蚀坑的不同形状和在表面的特定位置可将其分成三种类型,它们的起源可由一个关于腐蚀机制的模型加以解释.纯螺位错易于沿着由它结束的表面阶梯被腐蚀,形成一个小的Ga极性面以阻止进一步的纵向腐蚀,因而其腐蚀坑是位于两个表面阶梯交结处的截底倒六棱椎.纯刃位错易于沿位错线被腐蚀,因而其腐蚀坑是沿着表面阶梯分布的尖底倒六棱椎.极性在GaN的腐蚀过程中起了重要作用.     

用原子力显微镜和扫描电镜研究GaN外延层中的位错腐蚀坑

用原子力显微镜和扫描电镜相结合的方法表征了KOH腐蚀后的Si掺杂GaN外延层中的位错腐蚀坑.根据腐蚀坑的不同形状和在表面的特定位置可将其分成三种类型,它们的起源可由一个关于腐蚀机制的模型加以解释.纯螺位错易于沿着由它结束的表面阶梯被腐蚀,形成一个小的Ga极性面以阻止进一步的纵向腐蚀,因而其腐蚀坑是位于两个表面阶梯交结处的截底倒六棱椎.纯刃位错易于沿位错线被腐蚀,因而其腐蚀坑是沿着表面阶梯分布的尖底倒六棱椎.极性在GaN的腐蚀过程中起了重要作用.     

Sapphire substrate-transferred nitride-based light-emitting diode fabricated by sapphire wet etching technique

In order to investigate the influence of a sapphire substrate on the GaN-based light-emitting diode (LED) performance, sapphire-etched vertical-electrode nitride-based semiconductor (SEVENS) LEDs are fabricated by a sapphire wet etching technique. The performance of SEVENS-LEDs is substantially dependent on the presence of sapphire substrate. The light-output power of a SEVENS-LED with a microroughened surface structure and without a sapphire substrate (type-A) is not saturated up to a junction current as high as 300 mA, constituting a notable improvement relative to that (250 mA junction current) of SEVENS-LEDs with a 5 μm-thick sapphire substrate (type-B). The 200 mA light-output power of type-A SEVENS-LED is 1.8 times stronger than that of type-B SEVENS-LED. With increasing junction current, the variation of the peak wavelength is less for the type-A SEVENS-LED than for the type-B SEVENS-LED. These results imply that even a thin sapphire substrate on the SEVENS-LED affects the heat dissipation characteristic at high injection levels.     

Fabrication of sapphire rib waveguides using a femtosecond laser

We demonstrate a method for fabricating sapphire rib waveguides with femtosecond laser micromachining technology. Finite difference beam propagation method (FD-BPM) is applied to design sapphire rib waveguides. We explore the process of etching on a sapphire substrate surface via direct laser ablation. Rib waveguides that satisfies the dimensions of our design were fabricated. Actual light propagation performance is tested, and with the cut-back method, the insertion loss of 2.9±0.5 dB/cm is measured.     

GaN-Based LEDs With Mesh ITO p-Contact and Nanopillars

In this letter, the authors report the fabrication of GaN-based light-emitting diodes (LEDs) with mesh indium-tin-oxide p-contact and nanopillars on patterned sapphire substrate. Using hydrothermal ZnO nanorods as the etching hard mask, the authors successfully formed vertical GaN nanopillars inside the mesh regions and on the mesa-etched regions. It was found that 20-mA forward voltage and reverse leakage currents observed from the proposed LED were only slightly larger than those observed from the conventional LEDs. It was also found that output power of the proposed LED was more than 80% larger than that observed from conventional LED prepared on flat sapphire substrate.     

腔室状态对图形化蓝宝石衬底刻蚀工艺的影响

图形化蓝宝石衬底是近年来针对高度发光二极管的应用要求发展起来的一种新技术。通过利用自主研制的工业化感性耦合等离子体刻蚀机对图形化蓝宝石衬底的刻蚀工艺进行了研究。采用光学发射光谱仪和扫描电镜研究了PSS生产过程中腔室状态的变化对蓝宝石的刻蚀速率、选择比和图形形貌的影响。研究结果表明:随着反应腔累积放电时间的增加,刻蚀速率呈现下降趋势,选择比呈先上升然后下降的趋势。该趋势由反应腔室内表面上的沉积物所引起。     

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     

生长压力对MOCVD GaN材料晶体质量的影响

使用氮化物MOCVD外延生长系统,采用传统的两步生长法在76.2 mm c面蓝宝石衬底上生长了不同压力的GaN薄膜样品.研究发现提高高温GaN的生长压力,初期的三维生长时间增长,有利于提高GaN薄膜的晶体质量.同时采用XRD、PL谱和湿化学腐蚀方法研究了样品的位错特性,结果表明高压生长的样品能够降低位错密度,起到改善G...     

Structural Characterization of Homoepitaxial Blue GaInN/GaN Light-Emitting Diodes by Transmission Electron Microscopy

We perform a transmission electron microscopy (TEM) characterization of blue light-emitting diode epiwafers grown homoepitaxially on a c-plane GaN substrate and compare with such grown on sapphire. We find a threading dislocation (TD) density as low as 2 × 10⁸ cm⁻² in homoepitaxial growth, which is 1/30 of that in sapphire-based material. A unique type of inverted pyramid defect with diameter ∼650 nm was observed. It originates from the homo-interface in edge-type TDs. TDs were also found to be generated within the quantum wells without a precursor TD defect. Otherwise, high-resolution TEM suggests extremely homogeneous quantum wells and barriers in terms of composition and well width. Besides plan-view TEM, wet chemical etching on n-type GaN was carried out in hot phosphoric acid to evaluate the TD density more quickly. The two methods prove to be equivalent with respect of determined TD densities.     

Ultra uniform arrays of micro patterns on large area substrate by employing wet chemical etching

A wet chemical selective etching process is presented to delineate ultra-uniform micro patterns in the form of arrays of sensor chips of 4 mm×4 mm size in the matrix of 9×9 on a 3″ diameter silicon substrate with uniform physical and electrical characteristics. The selective etching of thin film is confined to the top area by masking its outer edges. This leads to uniform etching of the entire film leading to ultra-uniform delineation of arrays of micro patterns. The process has been verified over the selective etching of doped polysilicon in defining the polysilicon resistors and subsequently has been applied on realizing Ti/Au interconnecting lines using wet chemical etchant. Experimental results are presented with physical and electrical characteristics of the patterned structures in the statistical form over the substrate surface. SEM analysis is carried out for physical dimension measurement and standard deviation of 0.0040 is observed in polysilicon micro patterning. The process is competitive with reactive ion etching (RIE) in terms of yield, reliability and repeatability with cost effectiveness in a production environment. Methodology of ultra-uniform etching on entire substrate area is developed in support of the experimental results. The ratio of Top Surface Area (TSA) and Total Exposed Surface Area (TESA) is shown as crucial parameter for the uniform etching of thin films.