Composite metal substrate for thin film AIGaInP LED applications

Significance 

The rapid development of semiconductor technology offers a wide possibility of various systems implementation. In particular, light-emitting diodes (LEDs) have vast areas of applications including displays, automotive light and traffic signals. This can be attributed to their inherent physical characteristics that enable their efficient and reliable operation at both low current and voltages as well as severe conditions such as extremely high temperatures. Among the available light-emitting diodes, high-quality red-light light-emitting diodes are highly preferred for various applications. They are generally grown on lattice-matched GaAs substrate using metal-organic chemical vapor deposition. Unfortunately, the use of GaAs substrates for the fabrication of light-emitting diodes limits the light extraction efficiency of mostly the red and yellow light-emitting diodes due to the high light absorption nature of the material. Therefore, the development of alternative and efficient methods for fabrication of light-emitting diodes are highly desirable.

Recently, wafer bonding technology has been adopted for light-emitting diodes fabrication. It involves replacing the light absorbing GaAs substrate to enhance the efficiency. Additionally, the high brightness of the wafer is realized by transferring the epilayers to Si substrate and CuW metal substrates despite the difference in the thermal coefficients. The substrates are thereafter exposed to thinning action. Moreover, thinning of CuW substrates has remained a challenge. In a recently published literature, AlGaInP light-emitting diodes with patterned copper substrates have been fabricated. This, however, does not offer a perfect solution to the aforementioned challenges due to the cracking of the epilayers during thermal annealing processes.

To this note, researchers at the National Chiao Tung University led by Professor Ray-Hua Horng developed a new metal copper-invar-copper substrate based on the wafer bonding and epilayer transferring technologies. The copper-invar-copper substrate comprised of three layers: the top layer made of 20µm copper, middle Invar layer of 64µm and bottom layer made of 20µm copper. Additionally, the Invar layer was made up of iron and nickel metals mixed in the ratio 7:3. The authors computed the thermal expansion coefficient of the copper-invar-copper substrate and compared it to that of the GaAs substrate and AlGaInP epilayers. Eventually, the authors evaluated the performances of the resulting light-emitting diode packages with the copper-invar-copper substrate. The work is currently published in the research journal, Optics Express.

The authors observed that the coefficients of the copper-invar-copper substrate were approximately similar to that of GaAs substrate and AlGaInP epilayers. On the other hand, the high thermal conductivity of the copper-invar-copper substrate highly contributed to the excellent performance of the resulting light-emitting diodes. This closely followed a low redshift and high output power phenomenon. According to the authors, the copper-invar-copper substrate required a thorough cleaning by acid to improve the mechanical properties of the bonding material.

In summary, Professor Ray-Hua Horng and her research team successfully designed a novel composite metal substrate for the fabrication of thin-film AlGaInP light-emitting diode devices. Using the copper-invar-copper substrate to replace the original GaAs substrate prevented absorption of red light and by improving on the heat dissipation. Thus, the resulting light-emitting diodes exhibited normal electrical and optical properties. Considering that the epilayer could be transferred to the copper-invar-copper substrate without the need for thinning, copper-invar-copper is considered a promising substrate for the fabrication of high-efficiency thin-film light-emitting diodes with vertical electrodes for numerus applications.

About the author

Prof. Horng is a scientist active in the field of green photonics devices. She has introduced outstanding innovations to the process of fabrication of high performance LEDs and solar cells based on III-V quaternary semiconductors materials and III-V nitrides, covering all the aspects of development, from material growth and characterization to device design and fabrication, up to the stage of patent coverage and technology transfer.

Prof. Horng has also a remarkable record of publications, over 330 papers on SCI Journals and 500 papaers in Conference Proceedings, with an h index of 31 and 3969 citations of her published papers, and a rich portfolio of patents, about 155 (25 US and 130 domestic) of which 40 licensed to Companies. Dr. Horng received numerous awards recognizing her work on high-brightness LEDs. She has been awarded by the Ministry of Education of Taiwan for Industry/ University Corporation Project in 2002, by the Ministry of Science & Technology of Taiwan for the excellent technology transfer of high-power LEDs in 2006, 2008,2009, 2010 and 2011 by Chi Mei Optoelectronics for the first prize of Chi Mei Award in 2008, by the 2007 IEEE Region 10 Academia-Industry Partnership Award and distinguish research award of National Science Council of Taiwan in 2013. She became the Fellow of the Australian Institute of Energy since 2012, Fellow of the Institution of Engineering and Technology since 2013, Fellow of SPIE since 2014, Fellow of IEEE since 2015 and Fellow of OSA since 2016.

She has devoted special attention to the device technology as well as to the issues of interfacing with the system applications, thus achieving a number of contributions ranging from materials to processes, to thermal design and contact issues, to optics, and to packaging. Basically, the activity of Prof. Horng has been focused on material growth by MOCVD of III-V quaternary semiconductors, II-V nitride compounds, wide bandgap oxide materials and device fabrication of LEDs and semiconductor devices (containg HEMTs, deep UV photodiodes, deep UV phototransistor and gas sensors), and nano-technology fabrication processes for LEDs and high-efficiency solar cells.

One special achievement of Prof.Horng has been the smartcut technology and epilayer transfer for LEDs and solar cells, with re-use of the substrate. This technology has been developed in her laboratory and is described in several Journal papers, widely cited, as well as covered by international patents. Many patents were later transferred to manufacturing Companies in Taiwan, boosting them to the top international market positions (read below a letter of Endorsement).

Last but equally important, she has given contributions to electrical contacting, optical interfarces and thermal management for high power LEDs and concentrator solar cells.

Reference

Horng, R., Sinha, S., Lee, C., Feng, H., Chung, C., & Tu, C. (2019). Composite metal substrate for thin film AlGaInP LED applications. Optics Express, 27(8), A397.

Go To Optics Express

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