Efficiency enhancement of InGaN/GaN blue light-emitting diodes with top surface deposition of AlN/Al2O3

Significance 

The potential of indium gallium nitride/gallium nitride (InGaN/GaN) blue light-emitting diodes to have higher energy conversion efficiency has over the years been identified. Indium gallium nitride/gallium nitride light-emitting diodes grown on a c-plane sapphire substrate are known to possess a piezo-electric polarization field induced by the lattice mismatch between active indium gallium nitride and underlying gallium nitride layers. Moreover, the Wurtzite crystal structure of gallium nitride generates a spontaneous polarization field in the light-emitting diodes, which consequently forms tiled energy bands within the InGaN/GaN multi-quantum wells, leading to reduced spatial distribution of electron and hole wave functions and thus reduced radiative recombination rates. The techniques used to compensate such polarization fields require complicated device design, expensive substrates and skillful epitaxy techniques. Recently, stacked aluminum nitride/silica (AlN/Al2O3) showed potential to significantly improve the passivation quality. Unfortunately, no published reports on the influences of AlN/Al2O3 polarization layers on the performance of InGaN/GaN light-emitting diodes can be found in the existing plethora of literature.

Researchers led by Professor Zhenqiang Ma from University of Wisconsin-Madison in collaboration with Hong Kong University of Science and Technology scientists led by Professor Kevin Chen investigated the impact of plasma-enhanced atomic-layer deposition AlN/Al2O3 on the energy conversion efficiency of InGaN/GaN blue light-emitting diodes. They hoped that the AlN/Al2O3 stacked layers would significantly improve the light emitting diode-energy efficiency. Their work is currently published in the research journal, Nano Energy.

The research method employed entailed the use of X-ray photoelectron spectroscopy to characterize the surface potential changes inside the p-Gallium Nitride layer of InGaN/GaN light emitting diodes coated with AlN/Al2O3 stacked layers. The researchers then proceeded to fabricate the three types of gallium nitride light emitting diodes. Eventually, the energy efficiencies of the three types of fabricated LEDs wafers were characterized.

The authors made significant findings whereby the peak efficiency values of wall-plug efficiency, external quantum efficiency, and efficacy of the gallium nitride light emitting diodes were improved by 29%, 29% and 30%, respectively, and their corresponding efficiency droop rates were decreased by 13%, 6% and 3%, separately. In addition, the AlN/Al2O3 layers were noted to reduce the surface defect states of p-Gallium Nitride layer and enhance hole injection rate into the multi-quantum wells by increasing the surface potential of gallium nitride.

The study successfully reported the development of InGaN/GaN light emitting diodes with improved energy efficiency. Such significant energy improvements can be credited to the simple deposition of multifunctional ultrathin AlN/Al2O3 layers on top of p-type gallium nitride using remote plasma pretreatment and plasma-enhanced atomic-layer deposition. To be more specific, the AlN/Al2O3 stacked layers deposited on the gallium nitride: magnesium have overall improved the radiative recombination rate of the InGaN/GaN light emitting diodes and thus the improved light-emission efficiency. Therefore, the reported technique yields excellent results and should be adopted for further improvements.

Efficiency enhancement of InGaNGaN blue light-emitting diodes with top surface deposition of AlNAl2O3-Advances in Engineering

About the author

Kwangeun Kim received the B.S. and M.S. degrees in Electrical Engineering from Korea University, Seoul, Korea in 2009 and 2011, respectively, and M.S. degree in Electrical and Computer Engineering from the University of Wisconsin-Madison, Madison, WI, USA, in 2015, where he is currently pursuing the Ph.D. degree. Since 2013, he has been a Research Assistant with the University of Wisconsin-Madison. Between 2011 and 2013, he worked for Korean Standards Association, Seoul, Korea. His research interests focus on 1D, 2D, and 3D Si CMOS compatible process and wide band-gap semiconductor optoelectronics.

About the author

Dr. Dong Liu received her B.S. degree in optoelectronics engineering in 2009 and the Ph.D. in electrical engineering from Tsinghua University in Beijing, China in 2014. She has been a postdoctoral research associate in Prof. Zhenqiang Ma’s group in the Department of Electrical and Computer Engineering at the University of Wisconsin-Madison since 2014. Her research interests focus on wide-band gap material based optoelectronics devices, RF power electronics and large lattice mis-matched semiconductor heterostructures.

She is a recipient of the best Ph.D dissertation award in Tsinghua University. She is an author or a co-author of 29 peer-reviewed technical papers and book chapters related to her research and holds 1 US patent with 2 US patents pending. She serves as a technical reviewer for 6 international journals.

About the author

Jisoo Kim received the B.S. from Ajou University, Suwon, Korea and M.E. degrees from Korea Univeristy, Seoul, Korea, in 2011. Since September 2015, he is studying for a Ph.D. in electrical and computer engineering in University of Wisconsin-Madison. His research interests include heterojunction semiconductor device with 2port and three port device such as solar cell, LED, and HBT by nanomembrane transfer. Between 2011 and 2014, Jisoo worked as junior researcher in Shinsung solar energy Co. Ltd., Korea, conducting to improve efficiency of silicon solar cell.

About the author

Kevin J. Chen received the B.S. degree from Peking University, Beijing, China, and the Ph.D. degree from the University of Maryland, College Park, MD, USA. Prof. Chen joined HKUST in Nov. 2000, where he is currently a professor in the Department of Electronic and Computer Engineering at HKUST, he established the WIde-bandgap Semiconductor Electronics Laboratory (WISE Lab), focusing on technology development of GaN and SiC power and high-frequency devices and ICs.

He has led the invention of novel device concepts including composite-channel III-nitride HEMTs, double-heterojunction and double-channel III-nitride HEMTs, self-aligned enhancement-mode III-nitride HEMTs, enhancement-mode MISHFETs and planar integration of E/D-mode AlGaN/GaN HEMT, GaN-based MEMS using GaN-on-Patterned-Silicon (GPS), low-density-drain HEMT (LDD-HEMT), lateral field-effect rectifier, enhanced back barrier HEMT (EBB-HEMT), metal-2DEG tunnel junction FET (TJ-FET), GaN-based HEMTs on modified SOI substrate, photonic-ohmic drain FET (PODFET), GaN/SiC hybrid FET, SiC trench/planar MOSFET (TP-MOS).

For these inventions, 11 US patents on GaN device technology have been granted. Prof. Chen is an IEEE fellow and he has served as a Distinguished Lecturer for IEEE Electron Devices Society in area of advanced III-nitride technologies.

About the author

Mengyuan Hua received the B.S. degree in Physics from Tsinghua University, Beijing, China, in 2013. She then joined the Hong Kong University of Science and Technology (HKUST), Hong Kong, China, where she received the Ph.D. degree in Electronic and Computer Engineering in 2017 under the supervision of Prof. Kevin J. Chen. Currently, she is a post-doctoral fellowship at HKUST. Her research interests include GaN-based power device technology and device reliability and stability.

About the author

Zhenqiang (Jack) Ma received his B.S. degree in applied physics and B.E. degree in electrical engineering from Tsinghua University in Beijing, China in 1991. He received his M.S. degree in nuclear science and M.S.E. degree in electrical engineering from the University of Michigan, Ann Arbor in 1997, and the Ph.D. degree in electrical engineering from the University of Michigan, Ann Arbor in 2001. From 2001-2002, he was a member of the R&D team at Conexant Systems and later its spin-off, Jazz Semiconductor (now TowerJazz), in Newport Beach, CA. In 2002, he left Jazz to join the faculty of University of Wisconsin–Madison as an assistant professor in the Department of Electrical and Computer Engineering.

He is now a Lynn H. Matthias Professor in Engineering and a Vilas Distinguished Achievement Professor with affiliated appointments in four other departments and research institutes in engineering and medical school. His current interdisciplinary research covers electrical engineering, materials science and engineering, biomedical engineering, energy, health, and engineering physics.

His present research focuses on lattice-mismatched 3D-semiconductor heterostructures, microwave flexible electronics and bioelectronics. He is the author or co-author of over 470 peer-reviewed technical papers and book chapters related to his research and holds over 70 US, foreign and international patents. He is a recipient of PECASE. He is a fellow of AAAS, AIMBE, APS, IEEE, NAI and OSA.

Reference

Kwangeun Kim, Mengyuan Hua, Dong Liu, Jisoo Kim, Kevin J. Chen, Zhenqiang Ma. Efficiency enhancement of InGaN/GaN blue light-emitting diodes with top surface deposition of AlN/Al2O3. Nano Energy volume 43 (2018) pages 259–269.

 

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