March 2009 - May 2009
Publisher: Chairman Sheng-Lung Huang  Editors: Prof. Jui-che Tsai, Ms. Hsiao-wen Lin  June 30, 2009

Congratulations! GIPO Professor Ching-Fuh Lin receives the title of “Member of Asia-Pacific Academy of Materials”~


February GIPO Lecture Highlights


February 13th, 2009 (Friday), 10:30 am
Speaker: Dr. Lars Zimmermann (Technical University of Berlin, Germany)
Topic: Photonic integration in high-performance 0.13µm SiGe BiCMOS technology

Dr. Lars Zimmermann visited GIPO on February 13th, 2009 (Friday), and lectured in Room 103, Barry Lam Hall. His lecture on “Photonic integration in high-performance 0.13µm SiGe BiCMOS technology” was attended with enthusiasm by GIPO professors and students. Everyone learned much.

March “Photonics Forum” Lecture Highlights


March 3rd, 2009 (Tuesday), 1:30 pm
Speaker: Dr. Young-Kai Chen (Bell Lab., Alcatel-Lucent Technology, U.S.A.)
Topic: High speed electronics and optoelectronics for optic fiber communications 

Dr. Young-Kai Chen visited GIPO on March 3rd, 2009 (Tuesday). He lectured in Auditorium 101, Barry Lam Hall on the topic of “High speed electronics and optoelectronics for optic fiber communications”. The lecture was attended with enthusiasm by GIPO professors and students, and everyone learned much.

Dr. Young-Kai Chen (middle) with GIPO Chairman Sheng-Lung Huang (left) and GIEE Chairman Shey-Shi Lu (right)

April “Photonics Forum” Lecture Highlights


April 10th, 2009 (Friday), 2:30 pm
Speaker: Mr. Wei-Ming Huang (AU Optronics Corp., AC Technology Div. Director)
Topic: A Summary of TFT-LCD Industry and Technology


Mr. Wei-Ming Huang visited GIPO on April 10th, 2009 (Friday). He lectured in Room 113, Barry Lam Hall on the topic of “A Summary of TFT-LCD Industry and Technology”. GIPO professors and students attended the lecture with enthusiasm and learned much.



April 24th, 2009 (Friday), 2:30 pm

Speaker: Professor Chi-Kuang Sun ( GIPO, National Taiwan University)
Topic: Optical Virtual Biopsy Based On Least-Invasive Harmonic Generation Microscopy

Professor Chi-Kuang Sun was specially invited to speak in Auditorium 101, Barry Lam Hall on the topic of “Optical Virtual Biopsy Based On Least-Invasive Harmonic Generation Microscopy”. Professor Sun has made outstanding and innovative contributions in photonics and optoelectronics technology and received the title of IEEE Fellow. His research team’s groundbreaking achievements have not only been published by several noted journal, but have also been cited numerous times by important international academic media. His lecture incited eager participation from all GIPO professors and students, and everyone learned much.



~ The 3rd Seoul National University-National Taiwan University Student Workshop 2008 on Photonic Materials and Devices ~

Time: December 14th ~ 19th, 2008

Location: Seoul National University

Composed by Min-Yung Ke, GIPO Ph.D. candidate (Team Leader, representative student team)

Near the end of October, I received a letter from my professor, asking if I was interested in taking part in the 3rd National Taiwan University-Seoul National University Student Workshop. I replied “yes”, thinking that this would be an opportunity to do some travelling. However, at the 1st NTU pre-seminar meeting, I was unexpectedly elected the leader of the NTU team, responsible for planning and managing the event.

My interaction with Seoul began when I sent out an e-mail to the team leader of the Seoul group. After the initial greetings and polite exchanges, I realized that I had already met their leader back when we both took part in the 2nd Student Workshop. We exchanged MSN accounts immediately and began our intensive discussions and planning, which lasted until our NTU team flew to Korea on December 14th.

Our team was groggy and tired when we first landed, since we woke early to catch our flight. However, the cold air (0~ -2℃ ) in Korea woke us instantly. After excitedly buying Korea’s famous "banana milk", we waited for the SNU leader to come and pick us up from the airport, admiring the beauty of Korean girls while we waited.

Students and professors waiting at the airport

After our arrival at SNU and a short break, the SNU team leader and several students showed us around the campus. The campus is located in a mountainous area in the suburbs of Seoul, an area often frequented by hikers. Excluding the scattered high-rise buildings, the campus looked more like an ideal place for mountain climbing and hiking to us visitors from Taiwan. While touring and appreciating the campus scenery, we chatted with the Korean students, about student life and the rewards and challenges of our research.

On the SNU campus

After a good night's rest, the 3rd National Taiwan University-Seoul National University Student Workshop began the next morning. I listened to several reports on differing fields, delivered by both NTU and SNU students. I then noticed that, regardless of the outcomes of research, SNU students were better at expressing and putting forth the strengths of their research. With this ability, they were able to impress their listeners as they introduced their university.

Koreans are known to us, perhaps, as an energetic people. After planning the workshop itinerary with the SNU leader and interacting with SNU students during the workshop, I’ve also come to realize that they are not so different from people around us. They were enthusiastic and hospitable during our visit; during private discussions, they generously shared their research ideas with us. It seems to me that their life plans and goals are much the same as mine.

In the last few days after the seminar, we visited some ancient monuments and scenic areas in the suburbs of Seoul. We came to realize that the old Korea had been heavily influenced by Chinese culture. Nowadays their constant efforts and progress have made them a country to be respected, and SNU has also become one of the top 100 universities in the world. Participants of this year’s workshop were all doctoral students; they demonstrated positivity and self-confidence, fully identifying themselves with their studies and their environment. It seems to me that this positive attitude is less apparent in Taiwanese students. I feel that we can build our strength by learning from their attitude, and increase our ability to compete.

I would like to thank GIPO for providing us with this opportunity to take part in the workshop. Generally, during international conferences, we would merely deliver our reports and listen to others' reports, not interacting much with other participants. However, through this exchange, we interacted with SNU students and gained an understanding of the differences in thinking and in attitudes between students of different countries. Although I am back in Taiwan, I believe I have gained a lot from this workshop.




Composed by Chun-Da Liao, GIPO Ph.D. candidate

The 3rd National Taiwan University-Seoul National University Student Workshop took place at SNU, Korea, on December 15th, 2008. The seminar was focused on the application of photonic materials and components. Discussions covered five topics: optical characterization and modeling, wide band-gap semiconductors, OLED, infrared optoelectronics, and photonic devices. The four-day exchange event also included visits to Korea Advanced Nano Fab Center (KANC), Advanced Institute of Convergence Technology (AICT), and Inter-university Semiconductor Research Center (ISRC). In addition, tours exploring Korean culture and cities enhanced the exchange resulting from this event. We were provided with the opportunity to meet graduate students from other countries and to learn from each other, broadening our vision and horizons.

Korean graduate students like to chat about topics such as daily studying hours, interaction between advisors and students, students' salaries, and ways to ease pressure, just as Taiwanese graduate students do. Daily studying hours are about the same between the students of both universities. However, in Korea, a country renowned for its love of video games, students are unable to connect to any gaming website during class hours, which is not the case in Taiwan. Sports and music are common ways of alleviating pressure. Unlike Taiwan, however, Korean graduate students, and even professors, like to gather in small groups to drink a little and relax. In fact, there are bars on campus. As to research facilities, I think there are some things we could learn from SNU. Although NTU has plenty of research facilities and equipment, they are scattered all over campus, making them inconvenient to use. I believe that if we could build a large research center, bringing together all those facilities, and establish a comprehensive system of management, we would be more able to increase NTU's competitiveness in the international engineering field. As we can see from the development of industries of TFT-LCD, LED, OLED, and solar cells, Korea and Taiwan are generally on the same track in the area of photonics.

Participating professors and students at the workshop

Tour of the KANC

In addition to what was mentioned above, city tours allowed me to see more likeness between Korea and Taiwan. Some streets in downtown Seoul look very much like those in Taipei. For example, Seoul's Myeong-dong and Insa-dong look like Taipei's Ximen-ding and East Area (“dong” and “ding” seem close in meaning). Korean students like to visit these places during weekends and holidays as well. Seoul Tower, built on a hill, overlooks Seoul and its beautiful night view, just as Taipei 101 overlooks Taipei. The resemblance between Korean and Taiwanese cultures is even more apparent when visiting the art gallery and Changdeokgung Palace. With regard to writing and language, Chinese characters can be seen in many places in Korea, and some Taiwanese pronunciation is similar to Korean pronunciation. In terms of geography, both Taiwan and Korea are close to China. Therefore, it is easy to see the many resemblances between the two countries.

From this event, we have been inspired and learned a lot in terms of research and in terms of culture. I would like to thank the graduate students of SNU for their generous hospitality; Chairman Huang, Vice Chairman Lin and Professor Su for sharing their experiences during this trip.

Tour of the KANC

At the Seoul Museum of History



Characteristic Investigation of 2D Photonic Crystals with Full Material Anisotropy under Out-of-Plane Propagation and Liquid-Crystal-Filled Photonic-Band-Gap-Fiber Applications Using Finite Element Methods

Professor Hung-chun Chang

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

To effectively investigate the fundamental characteristics of two-dimensional (2D) photonic crystals (PCs) with arbitrary 3D material anisotropy under the out-of-plane wave propagation, we establish a full-vectorial finite element method based eigenvalue algorithm to perform related analysis correctly. The band edge diagrams can be conveniently constructed from the band structures of varied propagation constants obtained from the algorithm, which is helpful for the analysis and design of photonic band gap (PBG) fibers. Several PCs are analyzed to demonstrate the correctness of this numerical model. And the validity of those for the most complex PC with arbitrary 3D anisotropy is supported by related liquid-crystal-filled PBG fiber mode analysis, which demonstrates the dependence of transmission properties on the PBGs, employing a full-vectorial finite element beam propagation method (FE-BPM). (Optics Express, vol. 16, no. 26, pp. 21355–21368, 22 December 2008.)

Fig. 1. (a) The unit cell of a 2D PC with triangle-arranged liquid-crystal-filled holes in the silica. (b) Schematic definition of rotation angles for the liquid-crystal (LC) molecule.


Fig. 2. (a) The cross-section of an LC-core PCF. The PCF is assumed to be made of chalcogenide glass with the cladding region formed by triangle-arranged LC-filled holes. (b) The schematic geometry of the core region for (a), which is also filled with LCs.

Fig. 3. (a) The effective index and (b) the confinement loss of the y-polarized fundamental mode for the LC-core PCF of a = 2.26 μm with six rings of LC-filled holes, as shown in Fig. 2, obtained using the FE-BPM. The solid lines denote the PBG boundaries derived from the calculated band edge diagrams. Different colors are used to distinguish the results for different orientations of the LC molecules.






Enhanced and partially polarized output of a light-emitting diode with its InGaN/GaN quantum well coupled with surface plasmons on a metal grating

Professor C. C. Yang and Professor Yean-Woei Kiang

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

The enhanced and partially polarized output of a green light-emitting diode (LED), in which its InGaN/GaN quantum well (QW) couples with surface plasmons (SPs) on a surface Ag grating structure is demonstrated. Compared with an LED sample of no (flat) Ag coating, the total output intensity of an LED of SP-QW coupling can be enhanced by ~59 (~200) % when the grating period and groove depth are 500 nm and 30 nm, respectively. Also, a bottom-emission polarization ratio of 1.7 can be obtained under the condition of 15 nm in groove depth.

Fig. 1 LED bottom-emission spectra of samples A,B,and C(500).The subscript b in a sample notation represents bottom emission.In the insert, the setup for angle-dependent LED output intensity measurement is schematically shown.

Fig. 2 Total LED output intensities as functions of injection current of samples A, B, and C series. In the insert, the polarization ratios of bottom emission in various samples as functions of injection current are demonstrated. The subscript s in a sample notation represents total intensity.

Fig. 3 Total LED output intensities as functions of injection current of samples A’, B’, and D(500). In the insert, the polarization ratios of bottom emission in samples B’ and D(500) as functions of injection current are demonstrated.

Fig. 4 Total LED output intensities as functions of injection current of samples E, F, and G(500), including its two polarization components of bottom emission. The spectra of the corresponding LED outputs of bottom emission at 40 mA are shown in the insert.


Study on the decay mechanisms of surface plasmon coupling features with a light emitter through time-resolved simulations

Professor Yean-Woei Kiang and Professor C. C. Yang

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

The transient behaviors of the dipole coupling with surface plasmon (SP) features in an Ag/dielectric-interface grating structure in order to understand the characteristics of those dipole-coupling features are demonstrated. In particular, the major decay mechanisms of those coupling features can be identified. For comparison, the time-resolved behaviors of the resonant surface plasmon polariton (SPP) coupling feature on a flat interface are also illustrated. Among the three major grating-induced SP-dipole coupling features, two of them are identified to be localized surface plasmons (LSPs). The third one is a grating-assisted SPP, which shows two decay components, corresponding to the first stage of SPP in-plane propagation and the second stage of coupling system decay. In all the dipole coupling features, metal dissipation can dominate the energy relaxation process, depending on the assumption of damping factor. All the dissipation rates are proportional to the assumed damping factor in the Drude model of the metal. The dissipation rates of the LSP and resonant SPP features are about the same as the damping rate, implying their local electron oscillation natures. The dissipation rate of the grating-assisted SPP feature is consistent with theoretical calculation. In the LSP features under study, dielectric-side emission is prominent. The coupled energy in the grating-assisted SPP feature can be efficiently stored in the coupling system due to its low emission efficiency and effective energy confinement through grating diffraction.

Fig. 1. (a) Two-dimensional Ag/dielectric grating structure in the x-y plane. The dipole, Jx, is located 10 nm right below the center of a grating groove, which is defined as the origin, O, of the coordinate system. The flat interface structure is depicted by the dotted line along the x axis. (b) The dipole radiation power spectrum (continuous curve), the dielectric-side emission spectrum of the SP-dipole coupling system (dashed curve), the radiation power spectrum of the control case (dotted line near the bottom), and three source spectra (dashed Gaussian-like curves) for the three SP-dipole coupling features (A-C) in the grating structure. (c) The dipole radiation power spectrum (continuous curve), the dielectric-side emission spectrum of the SP-dipole coupling system (dashed curve), and the source spectrum (dashed Gaussian-like curve) for the SP-dipole coupling feature D in the flat-interface structure.


Fig. 2. Field strength (absolute value of Hz) distributions of the dipole-coupling features A-D in parts (a)-(d), respectively, at the individually chosen delay times for showing the broadest field distributions along the x axis when g = g0.


Fig. 3. Time-resolved field intensity profiles at point O of the four SP-dipole coupling features. The source profile is shown and labeled by S. The fitting lines for calibrating the decay times are plotted. The insert shows the linear-scale profiles for demonstrating the temporal peak positions. The damping factor g is set at g0.






Research Accomplishments in 2008, Wide Gap Semiconductor Laboratory

Professor Zhe-Chuan Feng

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

l “Structural and Optical Studies on Ion-implanted 6H-SiC Thin Films”, Z.C. Feng, et al., Thin Solid Films, 516, 5217-5226 (2008). Below are Raman and IR spectra for C+/Al+ co-implanted & annealed 6H-SiC


l     “Optical Investigation of GaSb Thin Films Grown on GaAs by Metalorganic Magnetron Sputtering”, Z.C. Feng, et al., Thin Solid Films, 516, 5493-5497 (2008).


Raman spectra from three MOMS-grown GaSb/GaAs (001) grown at substrate temperature of (a) 480, (b) 440 and (c) 400, and (d) a bulk GaSb.

Raman spectra from a MOMS-grown GaSb on GaAs (100) with Ts = 480, under different excitation wavelengths between 4579 and 5017 Å from an Ar+ laser.


l     “Emission dynamics of InAs self-assembled quantum dots with different cap layer structures”, L.M. Kong, Z.C. Feng, et al., Semiconductor Sci. & Technol., 23, 075044-8 (2008).

        Below are PL, TRPL and decay time-T plots of three InAs-QDs with different cap layer structures.

l       Book <III-NITRIDE DEVICES AND NANOENGINEERING>, Zhe Chuan Feng (National Taiwan University), Imperia College Press, London, 462 p., 2008., ISBN 978-1- 84816-223-5. This book, consisting of 15-well written review chapters, provides useful information to the device and nano-scale process, fabrication of LEDs, LDs, photodetectors and nano-devices, characterization, application and development on the III-Nitrides semiconductor devices and nano-engineering.

l       book chapter, “Structural and optical properties of InGaN/GaN multiple quantum well light emitting diodes grown by metalorganic chemical vapor deposition”, Z.C. Feng et al., in <<III-Nitride Devices and Nanoengineering>>, Chapter 3, pp.57-88, Imperial College Press, London, UK (2008).


In additions, Prof. Feng has in recent years published a series of specialized review books from world famous scientific publishers in USA, Germany, UK and Singapore, especially for wide gap semiconductors:

<III-NITRIDE SEMICONDUCTOR MATERIALS>, Zhe Chuan Feng (National Taiwan University), Imperia College Press, London, 440 p., 2006. ISBN 978-1-86094-636-3, (12-chapters)

<SiC Power Materials  Devices and Applications> by Zhe Chuan Feng (National Taiwan University), 450 p., 2004. ISBN: 978-3-540-20666-8, (11-chapters)

<Silicon Carbide: Materials, Processing and Devices> by Zhe Chuan FENG/Jian H. ZHAO, Taylor & Francis Books, New York, 416 p., 2003. ISBN: 9781591690238, (8-chapters)

<POROUS SILICON>, Z C Feng & R Tsu, World Scientific Publishing, Singapore, 488 pages.

<Semiconductor Interfaces, Microstructures and Devices: Properties and Application>, Zhe Chuan FENG, Institute of Physics Publishing, Bristol, 308 pages.

<Semiconductor Interfaces and Microstructures>, Zhe Chuan FENG, World Scientific Publishing, Singapore, 328 pages,



Organic-Inorganic Composite Thin-Film Solar Cells

Professor Ching-Fuh Lin

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

Solar cells attract great attention recently owing to the growing need for renewable energy. In particular, polymer solar cells offer the potential of large-scale power generation based on materials that provide flexibility, light weight, low-cost production and low-temperature fabrication. The most common and efficient material system so far for polymer devices is the one consisting of poly(3-hexylthiophene) (P3HT) and (6,6)-phenyl C61 butyric acid methyl ester (PCBM). However, the conventional bulk-heterojunction (BHJ) architecture has limitations in device stability. Exposure of the conventional solar cells to air leads to oxidation of the Al electrode and degradation of the indium tin oxide (ITO)/poly(3,4-ethylene dioxythio- phene): poly(styrene sulfonate) (PEDOT: PSS) interface because of the acidic nature of PEDOT:PSS.

To overcome the above difficulties, inverted configuration with semiconductor oxides is investigated in our Lab. The inverted structure has the advantage of improved stability by replacing both the low work function metal cathode and PEDOT:PSS. In addition, the environ- mentally friendly and low-cost ZnO is particularly well suited for this application as they can be deposited at low temperature. ZnO also provides hole blocking function. Furthermore, we develop low-temperature solution processes of transitional metal oxides deposited on top of the active layer to serve as the electron blocking layer. With the active layer sandwiched between the ZnO and the transitional metal oxide layers, the devices have the electrons and holes forced to transport separately toward opposite electrodes for efficient carrier collection, so greatly improving the power conversion efficiency (PCE) of solar cells.

Using P3HT/PCBM in the active layer, the inverted structure of polymer solar cells gives the PCE of 4.16 % (Fig. 1). The lifetime test shows that the PCE still retains 90% of the maximum value after 1000 hours of operation (Fig. 2). As the device is fabricated on the flexible polyester (PET) substrate, the PCE can also be 3.66%, the highest among the solar cells on flexible substrates. If the PV2000 is used for the active layer, the PCE is even as large as 5.13 % (Fig. 3), which is the highest among the solar cells with inverted structures.

Fig. 1 J-V curves of polymer solar cells using P3HT/PCBM.

Fig. 2 Reliability test of polymer solar cells using P3HT/PCBM.

Fig. 3 J-V curves of polymer solar cells using PV2000.


Narrow-Band Metal-Oxide-Semiconductor UV Photodetector

Professor Chee-Wee Liu

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

Si-based photodetector for narrow-band ultraviolet light (319nm) detection is demonstrated using a metal-oxide-semiconductor tunneling structure. By using appropriate selection of gate metal, the metal-oxide-semiconductor tunneling diode can detect the UV light. Due to the spectral dependence of absorption and reflection of the Ag as gate electrode, the narrow-band detection of ultra violet can be achieved. The photodetectors with 130nm thick Ag gate exhibit peak responsivities of 5.1mA/W at 319nm.

Fig. 1: (a) A Schematic structure of Metal-Oxide-Semiconductor tunneling photodetector. (b) Mechanism of the photocurrent formation. (c) Spectral responses of the MOS tunneling photodetector with the 70nm, 100nm, and 130nm Ag electrode. The inset shows the FWHM and the peak responsivity versus metal thickness.

The schematic structure of the MOS tunneling photodetector is shown in Fig. 1 (a). When the photons selected by the metal gate with energy larger than the bandgap of Si (1.12eV) illuminate on the gate electrode, the photo-generated electron-hole pairs in the depletion region can be separated by the built-in electric field in the depletion region (Fig.1 (b)). The photo-generated holes in the diffusion length away from the depletion edge can also reach the depletion region by diffusion. For the Ag thickness of 70nm, 100nm, and 130nm, the peaks of the spectral responses are located at 319nm with value of 17.3mA/W, 9.6mA/W, and 5.1mA/W, respectively (Fig. 1 (c)). The thickness of Ag can modulate the spectral response of photodetector. For thick Ag, the full width at half magnitude (FWHM) decreases but the responsivity also drops (the inset of Fig. 1 (c)).

In summary, the wavelength selection of metal-oxide-semiconductor detector is demonstrated by gate electrode. The gate electrode is not only used for reading out the electronic signal but also used as a filter to select the narrow band photons to enter the Si for further absorption. Due to the spectral dependence of absorption and reflection of the Ag as gate electrode, the UVB detector is demonstrated by Ag.


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