“The First Mesa Type Blue Light VICSEL and Droop Solutions” by Professor Chun-Yen Chang, National Chiao Tung University, Taiwan. IEEE Distinguished Lecturer.

Date:  November 30, 2012 (Friday)
Time:  1:45 pm – 2:30 pm
Venue:  PSDC, 1 Jalan Sultan Azlan Shah, 11900 Bayan Lepas, Penang, Malaysia

Abstract

Since the breakthrough of GaN material quality on c-plane sapphire, III-nitride material matured to a great success in LEDs and Laser diodes. So far, GaN-based edge emitting lasers have been demonstrated and applied in commercial products for high density optical storage, laser printing and display applications. However, the vertical cavity surface emitting lasers (VCSELs), with superior characteristics such as the single longitudinal mode emission, low divergence angle, and array capability, are still under development and currently gaining much attention. Recently, we have successfully demonstrated the achievement of first continuous wave (CW) current injection of GaN-based VCSEL with hybrid mirrors at room temperature in 2010. The laser structure consists of a ten-pair Ta₂O₅/SiO₂ distributed Bragg reflector (DBR), a 7λ-thick optical cavity, ten-pairs InGaN/GaN multiquantum wells with anAlGaN electron blocking layer, and a 29-pair AlN/GaN DBR. Under CW operation for a 2-µm aperture device, the threshold current was 9.7 mA and emission wavelength was approximately 412 nm. Due to above superior characteristics, GaN-based VCSEL is believed to play an important role in the future.

In addition, the visionaries have promised us a bright new world where efficient and cool white LEDs will replace the wasteful heaters known as incandescent light-bulbs. But, it’s hard to imagine LEDs dislodging incandescent and becoming to dominate the electric lighting industry, unless we can defeat “Droop” – the ways that the efficiency falls dramatically. The efficiency droop in InGaN-based LED was investigated in our research group. Electroluminescence results indicated that the light performance can be enhanced effectively when the conventional c-plane LED structures are replaced by non-polar m-plane substrate, (1-101) semi-polar GaN on Si, graded-composition EBL, and InAlGaN quaternary barriers. Furthermore, simulations showed that through our technical innovations higher radiative recombination rate and low efficiency droop can be realized at a high injection current. Using these approaches, we expect a boost to bring eco-friendly LEDs to our homes.

Speaker

Professor Chang served as President in NCTU for 8 years (1998-2006) and is National-Endowed-Chair Professor now. He received the IEEE life fellow (1987) and the IEEE third millennium medal in 2000. He is a member of Academia Sinica (1996) and Foreign Associate of the National Academy of Engineering, U.S.A (2000). He is the recipients of the Nikkei Asia Prize for science 2007 from Japan, and is also regarded as “the patriarch of Taiwan Semiconductor”.

In 1964, he and his colleagues established the nation first and the full facilities of Si planar technology research center at NCTU where they made the nation’s first Si planar transistor (1965), the first IC, MOSFET (1966) and surface stabilization and subsequently attracted worldwide attentions in MOS researches including Dwang Khang, G.L. Pearson, F.FANG, etc. and strongly forms the foundation of Taiwan Hi-tech development. For his continuous devotion, many of his students have since become founders of Hi-Tech enterprises and world renowned scientists.