Background story of the invention of efficient blue InGaN light emitting diodes (Nobel Lecture)

Shuji Nakamura discovered p‐type doping in Gallium Nitride (GaN) and developed blue, green, and white InGaN based light emitting diodes (LEDs) and blue laser diodes (LDs). His inventions made possible energy efficient, solid‐state lighting systems and enabled the next generation of optical storage. Together with Isamu Akasaki and Hiroshi Amano, he is one of the three recipients of the 2014 Nobel Prize in Physics. In his Nobel lecture, Shuji Nakamura gives an overview of this research and the story of his inventions *** .

     

Generation of high-power blue light in periodically poled LiNbO(3)

We report the generation of 450-mW average blue (473-nm) power by frequency doubling of a diode-pumped 946-nm Nd:YAG laser. We achieved pulsed operation at a high repetition rate (~160kHz) by driving the relaxation oscillations of the laser. A 40% conversion efficiency to the second harmonic was obtained in a single-pass, extracavity, first-order, quasi-phase-matched process in which periodically poled lithium niobate (period 4.5microm , thickness 0.5mm , and length 15mm) at 140 degrees C was used. The resulting high-power blue beam was circular in profile and nearly diffraction limited, indicating that photorefractive effects do not appear to limit device performance.     

Rutherford and Raman – Nobel laureates who had difficult early journeys to success

Two remarkable men, Ernest Rutherford in New Zealand and Chandrasekhara Raman in India, had very demanding early backgrounds from which most would fail to emerge with distinction. Yet, each rose to the top in science, Rutherford being awarded the Nobel Prize in Chemistry in 1908 and Raman the Nobel Prize in Physics in 1930. Their fascinating lives overlapped in interesting ways. There were many hurdles that each needed to overcome, mainly due to the early lack of both finance and good research facilities, and each required fortitude, resilience, industry and insight. The careers of both scientists should be an inspiration to today's students. Copyright © 2011 John Wiley & Sons, Ltd.     

Si(110)和Si(111)衬底上制备InGaN/GaN蓝光发光二极管

分别在Si(110)和Si(111)衬底上制备了In Ga N/Ga N多量子阱结构蓝光发光二极管(LED)器件.利用高分辨X射线衍射、原子力显微镜、室温拉曼光谱和变温光致发光谱对生长的LED结构进行了结构表征.结果表明,相对于Si(111)上生长LED样品,Si(110)上生长的LED结构晶体质量较好,样品中存在较小的张应力,具有较高的内量子效率.对制备的LED芯片进行光电特性分析测试表明,两种衬底上制备的LED芯片等效串联电阻相差不大,在大电流注入下内量子效率下降较小;但是,相比于Si(111)上制备LED芯片,Si(110)上LED芯片具有较小的开启电压和更优异的发光特性.对LED器件电致发光(EL)发光峰随驱动电流的变化研究发现,由于Si(110)衬底上LED结构中阱层和垒层存在较小的应力/应变而在器件中产生较弱的量子限制斯塔克效应,致使Si(110)上LED芯片EL发光峰随驱动电流的蓝移量更小.     

Quasi-homoepitaxial GaN-based blue light emitting diode on thick GaN templateQuasi-homoepitaxial GaN-based blue light emitting diode on thick GaN templateQuasi-homoepitaxial GaN-based blue light emitting diode on thick GaN templateQuasi-homoepitaxial GaN-based blue light emitting diode on thick GaN template

The high power GaN-based blue light emitting diode （LED） on an 80%tm-thick GaN template is proposed and even realized by several technical methods like metal organic chemical vapor deposition （MOCVD）, hydride vapor-phase epi- taxial （HVPE）, and laser lift-off （LLO）. Its advantages are demonstrated from material quality and chip processing. It is investigated by high resolution X-ray diffraction （XRD）, high resolution transmission electron microscope （HRTEM）, Rutherford back-scattering （RBS）, photoluminescence, current-voltage and light output-current measurements. The width of （0002） reflection in XRD rocking curve, which reaches 173＂ for the thick GaN template LED, is less than that for the conventional one, which reaches 258＂. The HRTEM images show that the multiple quantum wells （MQWs） in 80%tm- thick GaN template LED have a generally higher crystal quality. The light output at 350 mA from the thick GaN template LED is doubled compared to traditional LEDs and the forward bias is also substantially reduced. The high performance of 80-~m-thick GaN template LED depends on the high crystal quality. However, although the intensity of MQWs emission in PL spectra is doubled, both the wavelength and the width of the emission from thick GaN template LED are increased. This is due to the strain relaxation on the surface of 80%tin-thick GaN template, which changes the strain in InGaN QWs and leads to InGaN phase separation.     

Narrow-bandwidth diode-laser-based blue and ultraviolet light source

A compact, tunable and narrow-bandwidth laser source for blue and ultraviolet radiation is presented. A grating-stabilized diode laser at 922 nm is frequency-stabilized to below 100 Hz relative to a reference resonator. Injection of the diode-laser light into a tapered amplifier yields a power of 0.5 W. In a first frequency-doubling stage, more than 200 mW of blue light at 461 nm is generated by use of a periodically poled KTP crystal. Subsequent second-harmonic generation employing a BBO crystal leads to about 1 mW of ultraviolet light at 231 nm. Received: 12 August 2002 / Published online: 15 January 2003 RID="*" ID="*"Corresponding author. Fax: +49-89/32905-200, E-mail: christian.schwedes@mpq.mpg.de RID="**" ID="**"Present address: PTB, Bundesallee 100, 38116 Braunschweig, Germany     

Luminescence conversion of blue light emitting diodes

3 Al₅O₁₂:Ce³⁺(), has also been realized. Received: 6 February 1997/Accepted: 27 February 1997     

Ultrafast blue light emission from SiC nanowires

Cubic silicon carbide (SiC) nanowires are synthesized in a catalyst-assisted process. The nanowires with diameter of ～ 40 nm exhibit strong blue light emission at room temperature under ultraviolet (UV) femtosecond laser excitation. The photon energy of peak emission is higher than the energy bandgap of cubic SiC which shows involvement of quantum confinement effect. The ultrafast fluorescence is deconvoluted by Monte-Carlo method. The results show two ultrafast decay processes whose lifetimes are about 26 and 567 ps respectively. The mechanisms of such ultrafast processes are discussed.     

Organic blue light emitting materials based on spirobifluorene

Spirobifluorene derivative, which is useful for obtaining small molecule or polymer blue light emitting materials, has been prepared. To improve the solubility of final materials, long alkoxy side chains were introduced to spirobifluorene moiety. Coupling reaction with biphenyl led to small molecule blue light emitting material. A polymer blue light emitting material was obtained through Ni(0) mediated polymerization. Using vacuum deposition and spin coating methods, small molecule and polymer light emitting devices were fabricated and their device characteristics were investigated. In this paper, the detailed preparation methods of small molecule and polymer materials, and the device characteristics will be discussed.     

Generation of 740 mW of blue light by intracavity frequency doubling with a first-order quasi-phase-matched KTiOPO(4) crystal

We report on efficient intracavity frequency doubling of a cw diode-pumped Nd:YAG laser on the (4)F(3/2)?(4)I(9/2) laser transition at 946 nm. The nonlinear crystal used in the experiments was a first-order quasi-phase-matched flux-grown KTiOPO(4) crystal (period, 6.09mum ; thickness, 1 mm; length, 9 mm). The fluctuations in the generated second-harmonic wave were lower than 3% at output powers of as much as 500 mW. The overall optical-to-optical efficiency was 5.7%. A maximum output power of 740 mW of blue light was generated, which was stable for only 0.5 min. The decrease the output power at this power level was attributed to heating and thermal lensing in the periodically poled KTiOPO(4) crystal. The short-term behavior of the second-harmonic wave exhibited switching between a cw mode and chaotic intensity fluctuations.     

"沙尘中蓝紫色灯光"的奥秘

通过实验使学生对沙尘天气中蓝紫色光的产生原因有了初步的了解，培养了学生学习物理的兴趣．     

Stackable luminescent device integrating blue light emitting diode with red organic light emitting diode

We present a novel stackable luminescent device integrating a blue light emitting diode(LED)with a red organic LED(OLED)in series.The anode of the OLED is connected with the cathode of the LED through a via in the insulation layer on the LED.The LED–OLED hybrid device is electroluminescent and two electroluminescence(EL)peaks(the blue peak around 454 nm and the red peak around 610 nm)are observed clearly.The effect of the indium tin oxide(ITO)layer on the device performance is analyzed.Compared with the individual LED and OLED,their combination shows great potential applications in the field of white lighting,plant lighting,and display.     

Alterations in enamel remineralization in vitro induced by blue light

Blue light, especially from LED devices, is a very frequently used tool in dental procedures. However, the investigations of its effects on dental enamel are focused primarily on enamel demineralization and fluoride retention. Despite the fact that this spectral region can inhibit enamel demineralization, the effects of the irradiation on demineralized enamel are not known. For this reason, we evaluated the effects of blue LED on remineralization of dental enamel. Artificial lesions were formed in bovine dental enamel blocks by immersing the samples in undersaturated acetate buffer. The lesions were irradiated with blue LED (455 nm, 1.38 W/cm², 13.75 J/cm², and 10 s) and remineralization was induced by pH-cycling process. Cross-sectional hardness was used to asses mineral changes after remineralization. Non-irradiated enamel lesions presented higher mineral content than irradiated ones. Furthermore, the mineral content of irradiated group was not significantly different from the lesion samples that were not submitted to the remineralization process. Results obtained in the present study show that the blue light is not innocuous for the dental enamel and inhibition of its remineralization can occur.     

Quasi-phase-matched generation of tunable blue light in a quasi-periodic structure

We present what is to our knowledge a new approach to generating tunable blue light by cascaded nonlinear frequency conversion in a single LiTaO3 crystal. Simultaneous quasi-phase matching of an optical parametric generation process and a sum-frequency mixing process is achieved by means of structuring the crystal with a quasi-periodic optical superlattice. The spectral (wavelength tuning and bandwidth) and power characteristics of the blue-light generation are studied with a fixed-wavelength 532-nm picosecond laser and a wavelength-tunable nanosecond optical parametric oscillator (OPO) as the pump sources. By tuning the OPO wavelength, we could tune the blue output over approximately 20 nm. Temperature tuning of the blue output at a fixed pump wavelength of 532 nm was limited to approximately 1.5 nm. A maximum blue power of 15 microW was generated at a pump power of 0.5 mW, corresponding to an efficiency of 3%.     

Ultrasound-assisted blue light killing Vibrio parahaemolyticus to improve salmon preservation

Vibrio parahaemolyticus is a typical marine bacterium, which often contaminates seafood and poses a health risk to consumers. Some non-thermal sterilization technologies, such as ultrasonic field (UF) and blue light (BL) irradiation, have been widely used in clinical practice due to their efficiency, safety, and avoidance of drug resistance, but their application in food preservation has not been extensively studied. This study aims to investigate the effect of BL on V. parahaemolyticus in culture media and in ready-to-eat fresh salmon, and to evaluate the killing effectiveness of the UF combined with BL treatment on V. parahaemolyticus. The results showed that BL irradiation at 216 J/cm² was effective in causing cell death (close to 100%), cell shrinkage and reactive oxygen species (ROS) burst in V. parahaemolyticus. Application of imidazole (IMZ), an inhibitor of ROS generation, attenuated the cell death induced by BL, indicating that ROS were involved in the bactericidal effects of BL on V. parahaemolyticus. Furthermore, UF for 15 min enhanced the bactericidal effect of BL at 216 J/cm² on V. parahaemolyticus, with the bactericidal rate of 98.81%. In addition, BL sterilization did not affect the color and quality of salmon, and the additive UF treatment for 15 min did not significant impact on the color of salmon. These results suggest that BL or UF combined with BL treatment has potential for salmon preservation, however, it is crucial to strictly control the intensity of BL and the duration of UF treatment to prevent reducing the freshness and brightness of salmon.     

Quasi-homoepitaxial GaN-based blue light emitting diode on thick GaN template

The high power GaN-based blue light emitting diode (LED) on an 80-μ-thick GaN template is proposed and even realized by several technical methods like metal organic chemical vapor deposition (MOCVD), hydride vapor-phase epitaxial (HVPE), and laser lift-off (LLO). Its advantages are demonstrated from material quality and chip processing. It is investigated by high resolution X-ray diffraction (XRD), high resolution transmission electron microscope (HRTEM), Rutherford back-scattering (RBS), photoluminescence, current-voltage and light output-current measurements. The width of (0002) reflection in XRD rocking curve, which reaches 173" for the thick GaN template LED, is less than that for the conventional one, which reaches 258". The HRTEM images show that the multiple quantum wells (MQWs) in 80-μm-thick GaN template LED have a generally higher crystal quality. The light output at 350 mA from the thick GaN template LED is doubled compared to traditional LEDs and the forward bias is also substantially reduced. The high performance of 80-μm-thick GaN template LED depends on the high crystal quality. However, although the intensity of MQWs emission in PL spectra is doubled, both the wavelength and the width of the emission from thick GaN template LED are increased. This is due to the strain relaxation on the surface of 80-μm-thick GaN template, which changes the strain in InGaN QWs and leads to InGaN phase separation.