Browsing by Author "Zhao, Y."
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Item Open Access 48 W continuous-wave output from a high- efficiency single emitter laser diode at 915 nm(Institute of Electrical and Electronics Engineers, 2022-09-19) Liu, Y.; Yang, G.; Zhao, Y.; Tang, S.; Lan, Y.; Zhao, Y.; Demir, AbdullahImproving the power and efficiency of 9xx-nm broad-area laser diodes has a great help in reducing the cost of laser systems and expanding applications. This letter presents an optimized epitaxial structure with high power and conversion efficiency. Laser diodes with 230 μm emitter width and 5 mm cavity length deliver continuous-wave output power up to 48.5 W at 48 A, 30 °C, the highest power reported for 9xx-nm single emitter lasers so far. The slope efficiency is as high as 1.23 W/A due to a low internal optical loss of 0.31 cm−1 and a high internal efficiency of 96%. The maximum power conversion efficiency reaches 72.6% at 15.3 W and 67.3% at the operating power of 30 W under a heatsink temperature of 25 °C. Life test results show no failure in 1000 hours for 55 laser diodes.Item Open Access 808 nm broad-area laser diodes designed for high efficiency at high-temperature operation(Institute of Physics Publishing Ltd., 2021-09-21) Lan, Y.; Yang, G.; Liu, Y.; Zhao, Y.; Wang, Z.; Li, T.; Demir, AbdullahSemiconductor lasers with high power conversion efficiency (PCE) and output power are heavily investigated driven by more energy-efficient commercial applications. In this paper, an asymmetric broad area laser (A-BAL) design is studied and compared with a conventional symmetric broad area laser (S-BAL) design for 808 nm single emitter laser diodes. We present a comparative theoretical and experimental investigation by studying the thermal effects on the laser parameters. The output characteristics and efficiency loss paths for the designs were analyzed. The leakage of carriers was identified as the primary source of the PCE reduction with temperature. Suppressing this leakage by optimization of the A-BAL design, a record continuous-wave PCE of 68% at 25 °C and 60.4% at 75 °C were achieved for a single emitter laser with 10 W output power. These devices deliver high efficiency at high temperatures with reliable operation achieving 2000 h of an accelerated aging lifetime without failures.Item Open Access AC-driven, color-and brightness-tunable organic light-emitting diodes constructed from an electron only device(2013) Zhao, Y.; Chen, R.; Gao, Y.; Leck, K.S.; Yang X.; Liu, S.; Abiyasa, A.P.; Divayana, Y.; Mutlugun, E.; Tan, S.T.; Sun H.; Demir, Hilmi Volkan; Sun X.W.In this paper, a color- and brightness-tunable organic light-emitting diode (OLED) is reported. This OLED was realized by inserting a charge generation layer into an electron only device to form an n-i-p-i-n structure. It is shown that, by changing the polarity of applied voltage, only the p-i-n junction operated under positive bias can emit light and, by applying an AC voltage, emission from both junctions was realized. It is also shown that, by using a combination of blue- and red-emiting layers in two p-i-n junctions, both the color and brightness of the resulting white OLED can be tuned independently by changing the positive and negative amplitudes of the AC voltage. © 2013 Elsevier B.V. All rights reserved.Item Open Access Anisotropic stimulated emission from aligned CdSe/CdS dot-in-rods(IEEE, 2014-10) Gao, Y.; Ta, V. D.; Zhao, X.; Wang, Y.; Chen, R.; Zhao, Y.; Dang, C.; Sun, X.; Sun, H.; Demir, Hilmi VolkanAnisotropic optical properties of CdSe/CdS dot-in-rods loaded in a capillary tube are demonstrated, suggesting nanorods' alignment with a microfluidic approach. Polarized emissions from photoluminescence and whispering gallery mode lasing show promising applications for lighting and displays. © 2014 IEEE.Item Open Access COMD-free continuous-wave high-power laser diodes by using the multi-section waveguide method(SPIE - International Society for Optical Engineering, 2023-03-14) Demir, Abdullah; Ebadi, Kaveh; Liu, Y.; Sünnetçioğlu, Ali Kaan; Gündoğdu, Sinan; Şengül, Serdar; Zhao, Y.; Lan, Y.; Yang, G.; Zediker, Mark S.; Zucker, Erik P.Catastrophic optical mirror damage (COMD) limits the output power and reliability of laser diodes (LDs). The self-heating of the laser contributes to the facet temperature, but it has not been addressed so far. This study investigates a two-section waveguide method targeting significantly reduced facet temperatures. The LD waveguide is divided into two electrically isolated sections along the cavity: laser and passive waveguide. The laser section is pumped at high current levels to achieve laser output. The passive waveguide is biased at low injection currents to obtain a transparent waveguide with negligible heat generation. This design limits the thermal impact of the laser section on the facet, and a transparent waveguide allows lossless transport of the laser to the output facet. Fabricated GaAs-based LDs have waveguide dimensions of (5-mm) x (100-µm) with passive waveguide section lengths varied from 250 to 1500 µm. The lasers were operated continuous-wave up to the maximum achievable power of around 15 W. We demonstrated that the two-section waveguide method effectively separates the heat load of the laser from the facet and results in much lower facet temperatures (Tf). For instance, at 8 A of laser current, the standard laser has Tf = 90 oC, and a two-section laser with a 1500 µm long passive waveguide section has Tf = 60 oC. While traditional LDs show COMD failures, the multi-section waveguide LDs are COMD-free. Our technique and results provide a pathway for high-reliability LDs, which would find diverse applications in semiconductor lasers. © 2023 SPIE.Item Open Access Facet passivation process of high-power laser diodes by plasma cleaning and ZnO film(Elsevier, 2022-09-15) Lan, Y.; Yang, G.; Zhao, Y.; Liu, Y.; Demir, AbdullahPassivation of dangling bonds at the cleaved mirror facet and its durability are fundamental features of semiconductor lasers to obtain reliable operation with a long device lifetime. The high non-radiative recombination activity of the surface states needs to be controlled to prevent the Fermi level pinning before the deposition of mirror coating materials. Here, we report the incorporation of plasma cleaning of the facet and ZnO film as a passivation layer for the fabrication of high-power semiconductor lasers. The Argon plasma cleaning process was investigated to eliminate surface contamination without damaging the cavity surface. The ZnO passivation films were systematically studied by varying the chamber pressure and sputtering power of the radio frequency (RF) sputter coating process. We obtained homogeneous and dense ZnO films with high surface quality and optical absorption coefficient of zero. By incorporating the optimum plasma cleaning and passivation layer parameters, GaAs-based laser devices with significantly improved catastrophic optical mirror damage (COMD) power were achieved. COMD threshold was increased from 11.9 W to 20.7 W. The life test results demonstrate no failure for facet cleaned and passivated devices for more than 500 h, confirming the long-term effectiveness of the process for actual device integration.Item Embargo Guided lithium nucleation and growth on lithiophilic tin-decorated copper substrate(Elsevier Inc., 2022-08-04) Ye, L.; Zhang, C.; Zhou, Y.; Ülgüt, Burak; Zhao, Y.; Qian, J.Lithium metal is the ultimate anode choice for high energy rechargeable lithium batteries owing to its ultra-high theoretical capacity, however, Li dendrites and low Coulombic efficiency (CE) caused by disordered Li plating restrict its practical application. Herein, we develop an ultrathin Sn-decorated Cu substrate (Sn@Cu) fabricated by an electroless plating method to induce ordered Li nucleation and growth behavior. The lithiophilic Sn interfacial layer is found to play a critical role to lower the Li nucleation over-potential and promote fast Li-migration kinetics, and the underlying mechanism is revealed using the first principle calculations. Accordingly, a dense dendrite-free and Li deposition with large granular morphology is obtained, which significantly improved the CE and cycling performance of Li||Sn@Cu half cells symmetric cells. Symmetric cells using the Li-Sn@Cu electrode display a much-prolonged life span (>1200 h) with low overpotential (∼18 mV) at a high current density of 1 mA cm−2. Moreover, full cells paired with commercial LiFePO4 cathode (1.8 mAh cm−2) deliver enhanced cycling stability (0.5 C, 300 cycles) and excellent rate performance. This work provides a simple and effective way to bring about high efficiency and long lifespan substrates for practical applications.Item Open Access High efficiency 1.9 Kw single diode laser bar epitaxially stacked with a tunnel junction(IEEE, 2021-04-21) Zhao, Y.; Wang, Z.; Demir, Abdullah; Yang, G.; Ma, S.; Xu, B.; Sun, C.; Li, B.; Qiu, B.We report on the development of a 940-nm diode laser bar based on epitaxially stacked active regions by employing a tunnel junction structure. The tunnel junction and the device parameters were systematically optimized to achieve high output and power conversion efficiency. A record quasi-continuous wave (QCW) peak power of 1.91 kW at 25 °C was demonstrated from a 1-cm wide bar with a 2-mm cavity length at 1 kA drive current (200 μs pulse width and 10 Hz repetition rate). Below the onset of the thermal rollover, the slope efficiency was as high as 2.23 W/A. The maximum power conversion efficiency of 61.1% at 25 °C was measured at 300 A. Reducing the heatsink temperature to 15 °C led to a marginal increase in the peak power to 1.95 kW.Item Open Access High-power operation and lateral divergence angle reduction of broad-area laser diodes at 976 nm(Elsevier, 2021-04-28) Liu, Y.; Yang, G.; Wang, Z.; Li, T.; Tang, S.; Zhao, Y.; Lan, Y.; Demir, AbdullahBroad-area diode lasers with high output power and low lateral divergence angle are highly desired for extensive scientific and industrial applications. Here, we report on the epitaxial design for higher output power and a flared waveguide design for reduced divergence, which leads to high power operation with a low lateral divergence angle. A vertically asymmetric epitaxial structure was employed and optimized for low internal optical loss and high efficiency to realize high output power operation. Using a flared waveguide design, the lateral divergence angle was efficiently reduced by decreasing the number of high-order lateral optical modes significantly. The flared waveguide design introduces a smooth modification of the ridge width along the cavity without deteriorating laser performance. Based on the optimized epitaxial and waveguide design, we scaled the waveguide width to realize high continuous-wave power of 34.5 W at 25 °C. A low lateral divergence angle of 8° and high power conversion efficiency of 60% were achieved at the operating power level of 25 W. The life test data (30 A at 45 °C for 39 units, 0 failures in 1000 h) demonstrated reliable operation illustrating the efficient design for reduced lateral divergence angle and high operating power.Item Open Access Highly flexible, full-color, top-emitting quantum dot light-emitting diode tapes(IEEE, 2013) Yang X.; Mutlugün, Evren; Gao, Y.; Zhao, Y.; Tan, S.T.; Sun X.W.; Demir, Hilmi VolkanWe report flexible tapes of high-performance, top-emitting, quantum dot based, light-emitting diodes (QLEDs) with multicolor emission, actively working even when flexed. The resulting QLED tapes reach a high peak luminance level of 19,265 cd/m2. © 2013 IEEE.Item Open Access Low-cost, large-scale, ordered ZnO nanopillar arrays for light extraction efficiency enhancement in quantum dot light-emitting diodes(IEEE, 2014) Yang, X.; Dev, K.; Wang, J.; Mutlugün, E.; Dang, C.; Zhao, Y.; Tan, S. T.; Sun, X. W.; Demir, Hilmi VolkanWe report a QLED with enhanced light outcoupling efficiency by applying a layer of periodic ZnO nanopillar arrays. The resulting QLED reaches the record external quantum efficiency (EQE) of 9.34% in green-emitting QLEDs with a similar device structure.Item Open Access Solution Processed Tungsten Oxide Interfacial Layer for Efficient Hole-Injection in Quantum Dot Light-Emitting Diodes(Wiley-VCH Verlag, 2014) Yang, X.; Mutlugun, E.; Zhao, Y.; Gao, Y.; Leck, K. S.; Ma, Y.; Ke, L.; Tan, S. T.; Demir, Hilmi Volkan; Sun, X. W.A highly efficient and stable QLED using an inorganic WO3 nanoparticle film as a hole injection layer is demonstrated.The resulting WO3 nanoparticle-based QLEDs also exhibit superior performance compared to that of the present PEDOT:PSS-based QLEDs. The results indicate that WO3 nanoparticles are promising solution-processed buffer layer materials and serve as a strong candidate for QLED technology towards the practical applications in the next-generation lighting and displays. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.