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Research Interests

Our core research interests lie in exploring and understanding thin films and low dimensional nano-structured materials of wide band gap oxide semiconductors & dielectrics, constructing oxide hetero-structure or homo-structure, developing new applications for transparent electronic, energy-efficiency-related, and prospective optoelectronic devices. Additionally, my research interest also includes fundamental investigations on compound oxide properties and multifunctional material integration issues.

Our R&D interest motivated by the 3A (Aim, Ability and Action) strategy

Current research focuses on the following areas:
• Novel oxide semiconductor thin films and the electronic and optoelectronic applications
• High k oxide dielectric thin films and in circuit applications
• Planar structure and low-dimensional adaptive electronic devices
• Energy-related optical materials and devices: Electrochromic module and Solar thermal absorber

Current Research Progress
Topic 1—n-type oxide semiconductors and its applications
The development of thin film transistors (TFTs) based on large area transparent rigid or flexible substrates could promote macroelectronic technologies, and oxide semiconductor based TFTs have attracted ever-increasing attention as promising large-area backplane electronic devices for flat panel displays. We are making transparent conducting oxide thin films (Passive layer), transparent semiconducting thin films (Active layer), as well as high K oxide dielectric thin films, for the purpose of fabricating oxide-channel-based high mobility thin film transistors featuring low thermal budget and long-term stability.

Topic 2—p-type oxide semiconductors and its applications
TFTs based on transparent oxide semiconductors (TOSs) have attracted considerable research attention on basis of their good transparency, high field-effect mobility, making them possible to replace amorphous or/and poly-silicon in the area of consumer electronics. However, most of high mobility oxide semiconductors show n-type conduction; only a limited number of oxides exhibit p-type conduction with modest hole mobilities. SnO has gained much attention simply because it exhibits high hole mobility, comparable to other counterparts. It has been proposed that the valence band maxima (VBM) of SnO was mainly consisted of Sn 5s orbitals. Isotropic extended s orbitals constitute largely overlapped wave functions of the cations, which forms effective carrier conduction paths. As a result, SnO exhibits a fairly high hole mobility among p-type oxide semiconductors. Those properties make SnO a promising candidate utilized in the areas such as oxide based CMOS circuit, photovoltaics, sensors, and so on.

Topic 3—CMOS-like circuit based on oxide semiconductor
Oxide thin-film transistor (TFT)-based electronic components such as inverters and ring oscillators are appealing due to their low-cost, low-temperature fabrication, and ease of large-area processability. In addition to exploring high performance unipolar oxide TFTs, ambipolar thin film transistors (TFTs) based on one mother channel in one device with thereby simplified circuit design and fabrication processes (No separate patterning or/and doping steps needed), are gaining ever-increasing attention as an alternative approach to realizing integrated circuits. We succeed in fabricating an ambipolar transistor using tin mono-oxide (SnO) as a channel, which possesses the balanced electron and hole field-effect mobilities. A complementary metal oxide semiconductor (CMOS) - like inverter using the SnO dual operation transistors is demonstrated with a maximum gain up to 30 and long-term air stability, offering new opportunities for designing and constructing oxide-based logic circuits.

Topic 4—Electrochromic materials and modules
Electrochromism is the reversible and controllable change in transmittance or/and reflectance that is companied by an electrochemical oxidation-reduction reaction. It stems from the generation of different visible region electronic absorption bands on electrical field-induced switching between redox states. In the case of more than two redox states are electrochemically available, the electrochromic material may demonstrate several colors. Electrochromic materials and devices are of great interest in emerging technologies, where they can be used in smart windows to regulate the solar radiant energy, the anti-dazzling mirrors to engineer luminous reflectance, the temperature control devices to adjust the infrared emissivity, and so on. In our group, the correlation between the electrochromic performance and the film properties was investigated, and an all inorganic-based complementary electrochromic device was successfully fabricated.

Topic 5—Solar thermal absorber coatings
Solar thermal collectors have attracted a great deal of attention, since they can offer a pathway to a cost-competitive alternative to our traditional energy harvesting. The development of an efficient and reliable solar collector at an all incident solar radiation and simultaneously should have thermal losses by convection, conduction, and radiation that are as small as possible. The most attractive method of minimizing the radiation losses from a collector is the use of solar selective absorber. An efficient solar selective absorber is defined as having a high absorptance over the solar spectrum (0.3 µm < λ < 2.0 µm) and having a low emissivity (2.0 µm < λ < 25 µm) to reduce thermal radiative heat losses. A solar selective coating, in addition to having high absorptance (α) and low thermal emissivity (ε), must be stable at working temperatures and resistant to atmospheric corrosion for long term run.
We have developed Chromic-based absorber coatings for low temperature solar thermal application, and then the related thermal aging mechanisms have been proposed. The coating exhibits a high absorptivity (α) of 0.947 and a low emissivity (ε) of 0.05 at 80℃. Then, the dependence of optical properties, microstructure, and chemical composition of the coatings before and after thermal treatment was investigated. It was revealed that the copper diffusion whether throughout the entire stacked layers or near the interface region, the chemical interactions adjacent to the interface, and the interface width broadening are the Achilles’ heel for the solar thermal coatings to sustain high thermal stability.