Enhancing the output power of GaN-based LEDs grown on wet-etched patterned sapphire substrates

GaN-based light-emitting diodes (LEDs) with emitting wavelength of 450 nm were grown on patterned sapphire substrates (PSSs) fabricated by chemical wet etching. The crystallography-etched facet was {1-102} R-plane with a 57/spl deg/ against {0001} C-axis and had superior capability for enhancing light extraction efficiency. The light output power of the PSS LED was 1.15 times higher than that of the conventional LED at an injection current of 20 mA. The output power and external quantum efficiency were estimated to be 9 mW and 16.4%, respectively. The improvement was attributed not only to geometrical shapes of {1-102} crystallography-etched facets that efficiently scatter the guided light to find escape cones, but also to dislocation density reduction by adopting the PSS growth scheme.     

Efficiency improvement of near-ultraviolet InGaN LEDs using patterned sapphire substrates

The use of conventional and patterned sapphire substrates (PSSs) to fabricate InGaN-based near-ultraviolet (410 nm) light-emitting diodes (LEDs) was demonstrated. The PSS was prepared using a periodic hole pattern (diameter: 3 /spl mu/m; spacing: 3 /spl mu/m) on the (0001) sapphire with different etching depths. From transmission-electron-microscopy and etch-pit-density studies, the PSS with an optimum pattern depth (D/sub h/=1.5 /spl mu/m) was confirmed to be an efficient way to reduce the thread dislocations in the GaN microstructure. It was found that the output power increased from 8.6 to 10.4 mW, corresponding to about 29% increases in the external quantum efficiency. However, the internal quantum efficiency (@ 20 mA) was about 36% and 38% for the conventional and PSS LEDs, respectively. The achieved improvement of the output power is not only due to the improvement of the internal quantum efficiency upon decreasing the dislocation density, but also due to the enhancement of the extraction efficiency using the PSS. Finally, better long-time reliability of the PSS LED performance was observed.     

Increased effective reflection and transmission at the GaN-sapphire interface of LEDs grown on patterned sapphire substrates

The effect of patterned sapphire substrate (PSS) on the top-surface (P-GaN-surface) and the bottom-surface (sapphire-surface) of the light output power (LOP) of GaN-based LEDs was investigated, in order to study the changes in reflection and transmission of the GaN-sapphire interface. Experimental research and computer simulations were combined to reveal a great enhancement in LOP from either the top or bottom surface of GaN-based LEDs, which are prepared on patterned sapphire substrates (PSS-LEDs). Furthermore, the results were compared to those of the conventional LEDs prepared on the planar sapphire substrates (CSS-LEDs). A detailed theoretical analysis was also presented to further support the explanation for the increase in both the effective reflection and transmission of PSS-GaN interface layers and to explain the causes of increased LOP values. Moreover, the bottom-surface of the PSS-LED chip shows slightly increased light output performance when compared to that of the top-surface. Therefore, the light extraction efficiency (LEE) can be further enhanced by integrating the method of PSS and flip-chip structure design.     

Lifetime Tests and Junction-Temperature Measurement of InGaN Light-Emitting Diodes Using Patterned Sapphire Substrates

The authors demonstrate nitride-based blue light-emitting diodes with an InGaN/GaN (460 nm) multiple quantum-well structure on the patterned sapphire substrates (PSSs) compared with conventional sapphire substrates (CSSs) using metal-organic chemical vapor deposition. According to full-width at half-maximum of high-resolution X-ray diffraction and transmission electron microscopy micrographs, the dislocation density of GaN epilayers grown on the PSS was lower than those of the CSS. It was found that the output power of devices on PSS was 26% larger than that of CSS. The lifetime defined by 50% loss in output power was 590 and 305 h at 85 degC for the PSS and CSS, respectively. It was also found that the junction temperature and thermal resistance were smaller for the PSS. These improvements are attributed to the reduction in dislocation density using PSS structure     

Influence of GaN material characteristics on device performance for blue and ultraviolet light-emitting diodes

An analysis of blue and near-ultraviolet (UV) light-emitting diodes (LEDs) and material structures explores the dependence of device performance on material properties as measured by various analytical techniques. The method used for reducing dislocations in the epitaxial III-N films that is explored here is homoepitaxial growth on commercial hybride vapor-phase epitaxy (HVPE) GaN substrates. Blue and UV LED devices are demonstrated to offer superior performance when grown on GaN substrates as compared to the more conventional sapphire substrate. In particular, the optical analysis of the near-UV LEDs on GaN versus ones on sapphire show substantially higher light output over the entire current-injection regime and twice the internal quantum efficiency at low forward current. As the wavelength is further decreased to the deep-UV, the performance improvement of the homoepitaxially grown structure as compared to that grown on sapphire is enhanced.     

图形衬底对InGaN/GaN多量子阱太阳能电池性能的提升

In this paper, the enhanced performance of InGaN/GaN multiple quantum well solar cells grown on patterned sapphire substrates （PSS） was demonstrated. The short-circuit current （Jsc） density of the solar cell grown on PSS showed an improvement of 60%, compared to that of solar cells grown on conventional sapphire substrate. The improved performance is primarily due to the reduction of edge dislocations and the increased light absorption path by the scattering from the textured surface of the PSS. It shows that the patterned sapphire technology can effectively alleviate the problem of high-density dislocations and low Jsc caused by thinner absorption layers of the InGaN based solar cell, and it is promising to improve the efficiency of the solar cell.     

Optical and Structural Properties of InGaN–AlGaN Ultraviolet Light-Emitting Diodes

We fabricated and investigated the performances of InGaN–AlGaN ultraviolet (UV) light-emitting diodes (LEDs) emitting at 380 nm. The output power of a conventional LED, a patterned sapphire substrate LED (PSS LED), and a PSS flip-chip LED (PSS FCLED) were about 0.94, 1.86, and 5.18 mW, respectively, at a forward injection current of 20 mA. These results indicate that the light output–powers of the PSS LED and PSS FCLED were enhanced as much as 97% and 451% compared to the conventional LED. Subsequent optical simulations confirm the remarkable enhancements in optical power of the PSS FCLED at UV wavelengths.      

六棱锥衬底旋转角影响LED效率的模拟探究

以正六棱锥型图形化蓝宝石衬底GaN基LED为研究对象,设计并探讨了正六棱锥图案在排布过程中旋转角的变化对LED出光效率的影响,得出各面光通量随旋转角变化的规律:在0°～30°范围,随着旋转角的增大,总光通量与顶部光通量有下降趋势,底部光通量有增长趋势。当六棱锥旋转角在0°～6°范围内时,LED芯片的总光通量和顶部光通量均有最优值。综合考虑,旋转角为0°～6°的六棱锥型图形衬底对正装LED的出光效率有最佳的优化效果。     

460-nm InGaN-Based LEDs Grown on Fully Inclined Hemisphere-Shape-Patterned Sapphire Substrate With Submicrometer Spacing

This letter investigates 460-nm InGaN-based light-emitting diodes (LEDs) grown on a hemisphere-shape- patterned sapphire substrate (HPSS) with submicrometer spacing. The full-width at half-maximum of the (102) plane rocking curves for GaN layer grown on a conventional sapphire substrate (CSS) and HPSS are 480 and 262 arcsec, respectively. Such improvement is due to the reduction of the pure edge threading dislocations. At the forward current of 20 mA, the light output power of the LEDs grown on CSS and HPSS were 4.05 and 5.86 mW, respectively. This improvement of 44% light-output power can be attributed to the improved quality of the material and the increase of the light extraction by the fully inclined facets of the HPSS.     

III-Nitride-Based Light-Emitting Diodes With GaN Micropillars Around Mesa and Patterned Substrate

In this paper, the textured-sidewall mesa and GaN microsize pillars (?-pillars) around the mesa region were fabricated on III-nitride light-emitting diodes (LEDs) with a patterned sapphire substrate (PSS). We demonstrated that the light-waveguide mode outside the mesa region of III-nitride LEDs could be disrupted by a GaN ?-pillar around the mesa region and PSS. We found that the power enhancement of LEDs with textured sidewall, ?-pillars around the mesa, and PSS from ray-tracing simulation was about 65% larger than that of conventional LEDs. It was found that we could achieve a high power enhancement of about 60% of LEDs with textured sidewall, ? -pillars around the mesa, and a patterned substrate, and it was close to the result of simulation. It was also found that the light intensity outside the mesa region with ? -pillars of LEDs with or without a patterned substrate would decay in proportion to the distance away from the mesa edge, by studying the light emission intensity image of the whole LEDs. The decay lengths for the textured sidewall and ?-pillars around the mesa LEDs with or without a patterned substrate are 12 and 17 ?m, respectively. We understand that the light outside the mesa region could be extracted earlier by introducing the GaN ?-pillars and patterned substrate together.     

Enhanced output power of near-ultraviolet InGaN-GaN LEDs grown on patterned sapphire substrates

Near-ultraviolet nitride-based light-emitting diodes (LEDs) with peak emission wavelengths around 410 nm were fabricated onto c-face patterned sapphire substrates (PSS). It was found that the electroluminescence intensity of the PSS LED shown 63% larger than that of the conventional LED. For a typical lamp-form PSS LED operating at a forward current of 20 mA, the output power and external quantum efficiency were estimated to be 10.4 mW and 14.1%, respectively. The improvement in the light intensity could be attributed to the decrease of threading dislocations and the increase of light extraction efficiency in the horizontal direction using a PSS.     

图形化蓝宝石衬底GaN基LED的研究进展

蓝宝石衬底作为发光二极管最常用的衬底,经过不断发展,在克服其与GaN间晶格失配和热膨胀失配问题上,研究人员不断提出解决方案。近期发展起来的图形化衬底技术,除了能减少生长在蓝宝石衬底上GaN之间的差排缺陷,提高磊晶质量以解决失配问题,更能提高LED的出光效率。从衬底图形的形状、尺寸、制备工艺出发,回顾了图形化蓝宝石衬底GaN基LED的研究进展,详细介绍了近年来关于图形化衬底技术与其他技术在提高LED性能方面的结合,总结了图形化蓝宝石衬底应用于大尺寸芯片的优势,并对其未来在大功率照明市场的应用进行了展望。     

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。     

Enhanced Light Extraction From Triangular GaN-Based Light-Emitting Diodes

This study investigated the characteristics of a triangular light-emitting diode (LED) and compared it to a standard quadrangular LED. The total radiant flux from the packaged triangular LED increased by 48% and 24% at input currents of 20 and 100 mA, respectively, compared to that of a quadrangular LED which was grown on patterned sapphire substrate. In light far-field beam distribution, the light extraction in the horizontal direction of the LED was much higher than that of the quadrangular LED due to the enhancement of light emission from the side walls of the triangular LED.     

Improved ESD voltage by inserting floating metal ring in GaN-based light emitting diodes

Improvement of the electrostatic discharge (ESD) voltage in an InGaN/GaN blue light emitting diode (LED) grown on sapphire substrate is presented by inserting floating metal near the n-electrode. ESD voltages about four times larger than previously observed are experimentally obtained for LEDs with floating metal compared to those without.     

Light Output Enhancement of InGaN Light-Emitting Diodes Grown on Masklessly Etched Sapphire Substrates

A maskless wet-etching method is used to prepare patterned sapphire substrates for enhancing the output power of InGaN light-emitting diodes (LEDs). Blue LEDs grown on the patterned sapphire substrates exhibit an output power of 24.9 mW, which is 19.4% higher than that of the devices grown on flat substrates. The uniformity of the optical and electrical properties of LEDs across a 2-in wafer is slightly improved as well.      

Si衬底氮化物LED器件的研究进展

通过对比分析目前氮化物LED的三种主要衬底即蓝宝石、SiC与Si的技术特点,指出了发展Si衬底LED的重要意义。详细介绍了目前国内外Si衬底LED的研究现状,解析了在Si衬底上制备LED的多种新型技术,主要包括以提高薄膜沉积质量为目的的缓冲层技术、激光脱离技术、图案掩模技术、阳极氧化铝技术,以及以提高光提取率为宗旨的镜面结构技术和量子阱/量子点技术。这些新型技术与传统的MOCVD,HVPE,MBE等制备技术相结合,在很大程度上克服了Si衬底的不足,使Si衬底上氮化物LED展现出广阔的发展前景。     

Transfer of GaN-Based Light-Emitting Diodes From Silicon Growth Substrate to Copper

III-nitride light-emitting diodes (LEDs) grown on Si (111) substrates have the potential of low-cost manufacturing for solid-state lighting and display, by taking advantage of the well-developed IC technologies of silicon. In this letter, LEDs grown on silicon substrates were transferred onto copper substrates, to maximize light extraction and heat dissipation. On Si substrates, $hbox{300} times hbox{300} muhbox{m}^{2}$ multiple quantum well InGaN LEDs were first grown and processed. The top surface of the fabricated devices was then temporarily bonded to a sapphire wafer and the Si substrate was chemically etched. Ti/Al/Ti/Au layers were deposited on the backside of LEDs. An 80-$muhbox{m}$ -thick copper layer was electroplated and the temporary bonding was removed, resulting in LEDs on copper substrate. The optical output power of LEDs on copper increased by $sim$ 70% as compared to that of the LEDs on silicon. The improved performance was attributed to the removal of the light-absorbing Si substrate and the good thermal conductivity of copper.      

Improved optical performance of GaN grown on pattered sapphire substrate

An improved GaN film with low dislocation density was grown on a C-face patterned sapphire substrate (PSS) by metalorganic chemical vapor deposition (MOCVD). The vapor phase epitaxy starts from the regions with no etched pits and then spreads laterally to form a continuous GaN film. The properties of the GaN film have been investigated by double crystal X-ray diffraction (DCXRD), atomic force microscopy (AFM) and photoluminescence (PL), respectively. The full-width at half-maximum (FWHM) of the X-ray diffraction curves (XRCs) for the GaN film grown on PSS in the (0002) plane and the (10(1)2) plane are as low as 312.80 arcsec and 298.08 acrsec, respec-tively. The root mean square (RMS) of the GaN film grown on PSS is 0.233 nm and the intensity of the PL peak is comparatively strong.     

图形衬底上MOCVD生长光学性质改进的GaN

An improved GaN film with low dislocation density was grown on a C-face patterned sapphire substrate （PSS） by metalorganic chemical vapor deposition （MOCVD）. The vapor phase epitaxy starts from the regions with no etched pits and then spreads laterally to form a continuous GaN film. The properties of the GaN film have been investigated by double crystal X-ray diffraction （DCXRD）, atomic force microscopy （AFM） and photoluminescence （PL）, respectively. The full-width at half-maximum （FWHM） of the X-ray diffraction curves （XRCs） for the GaN film grown on PSS in the （0002） plane and the （1012） plane are as low as 312.80 arcsec and 298.08 acrsec, respectively. The root mean square （RMS） of the GaN film grown on PSS is 0.233 nm and the intensity of the PL peak is comparatively strong.