四族材料 (Si, Ge, Sn) 分子束磊晶實驗室
Research highlights and Achievements
My work encompasses a range of areas based on group-IV materials, working mainly in three areas: (a) epitaxy growth of different type of heterostructure made of Si, Ge, and Sn using Molecular Beam Epitaxy system (MBE), (b) fabrication on optic and electronic devices, and (c) optoelectronic for the monolithic integration with high-speed Si electronics (so-called super chip). Here, I like to highlight two programs in which we are among the leading groups in the fields and our results have significant impact in the respective fields.
Si-based photonic is an emerging topic in both academia and industry, driven by the need for the integration with Si electronics to enhance the performance of optoelectronic systems. In this program, an all-group-IV photonic device based on a direct bandgap group-IV material is proposed aiming to be applied in various areas. A relatively new material system comprising of group IV materials, i.e., Si and Ge incorporated with another group-IV element, Sn, is developed. Direct bandgap group IV material (SiGeSn) is achieved and those photonic devices needed for the optoelectronic integration are demonstrated. The notable achievements are: (i) the first state-of-the-art Sn-based group-IV light-emitting diode operating at the near-infrared region with direct bandgap emission (Editor’s Pick on Semiconductor Research from APL (2014)), (ii) GeSn-based photodetector with best clarity at the near- to middle-infrared band, and (iii) the world’s first GeSn-based imager chip (320 pixel´ 256 pixel) operated at the near- to middle-infrared regions (Figure 1.). These results create new opportunities for researchers as well as provide the platform for the monolithic integration of Si-based electronic devices for forming the group-IV-based optoelectronic chip that will, over time, be more common in the near future.
Figure 1: (a) Light bulb image operated at a low power of 10 W taken by a cell phone. The image shows the shape of the tungsten filament located at the center. (b) Light bulb image taken by our GeSn-based diode array (320 diode ´ 256 diode). The image shows the capability of imaging and “displaying” of the thermal profile of the filament (solid arrow line) and the reflection of the inner surface of the light bulb (dashed arrow lines).
For the second program, we work on SiGe-based nanostructures and a new type of pattern－wrinkles, is first proposed and demonstrated as illustrated schematically in Figure 2. This new type of structure is different from those conventional semiconductor nanostructure formed by self-assemble process such as quantum dots etc. The pattern is fabricated by standard processing techniques which are characterized by defined dimension ranging from micro- to nanometer-scale. In showing the wrinkle pattern, not only of exploration of the fabrication methods, the fundamental physical properties of the wrinkles has also been established. This leads to the finding of several novel properties. For instance, the electrical properties of the film is altered transformed from a two dimensional plane into a one dimensional trajectory at the wrinkled edge giving an electrical characteristic similar to that of electrical diode. This nanostructure constitutes an alternative method for creating a potential in a low-dimensional structure and it shows new findings that would impact the nanosciences. A further development aimed at devices is in progress. If this is achieved, it can provide new structure for serving as electrical diode.
Fig. 2. (a) Schematic plot of the wrinkled structure. The structure is characterized by a lateral etching depth (h), spatial wavelength (λ), and amplitude (A). Carriers (red circle) move along the one dimensional wrinkled edge giving the electrical characteristic of electric diode. (b) AFM image of the wrinkles, showing that wrinkles are formed at the edge of channel.