Byeong-Hoon Cho

A highly sensitive and low‐noise IR photosensor based on a‐SiGe as a sensing and noise filter: Toward large‐sized touch‐screen LCD panels

— The a-SiGe TFT photosensor for embedded touch-screen panels (TSPs) was characterized by comparison with an a-Si sensor. The photoresponse of an a-SiGe sensor at a 850-nm wavelength was much higher than that of a-Si, indicating that a-SiGe is a strong candidate material for an IR sensor. In order to increase the signal-to-noise ratio, the incident visible light was filtered by incorporating a bandpass-filter layer. An a-SiGe IR-sensor-embedded LCD panel was successfully demonstrated, showing an excellent multitouch property independent of ambient-light conditions. This technology can be widely used in multifunctional TSPs.

Characteristics of a-SiGe:H Thin Film Transistor Infrared Photosensor for Touch Sensing Displays

Photo-generation properties in an amorphous SiGe:H thin film transistor (TFT) were characterized by analyzing the electrical performances under illumination. The a-SiGe:H TFT showed a higher photo sensitivity at the wavelength of IR regime, and as a-SiGe:H layer was thicker, the generated photo currents proportionally increased due to the higher photon absorption. The increase of Ge composition led to the reduction of optical energy band gap. However, the photo sensitivity was not increased with lowering of energy band gap due to the creation of defects in the layer. The photo generation was dependent on the geometry of TFT, such as channel width and length. In particular, it was observed that regions under the source/drain electrode played a critical role in generating the photo currents which was demonstrated by technology computer-aided design simulation. Based on these, the generation of photo current and the photo field effect in a-SiGe:H TFT were interpreted using band diagrams. A-SiGe:H IR photosensor-embedded liquid crystal display panel was successfully demonstrated, indicating that these can be useful to broad use in the photo-type touch sensor, photo detector, and solar cell devices.

Effects of the optical energy bandgap and metal work function on the contact resistivity in a-SiGe : H

Amorphous silicon based materials, especially a-SiGe : H, have provided a variety of applications in display backplane and sensor materials. The ultimate goal is the development of device architectures that offer improved properties and functionality. In this article, the electrical contact resistivity (ρc) of a-SiGe : H is investigated in terms of the optical energy bandgap modulated by Ge incorporation and the work function of the contact metals. Firstly, the ρc is found to be dependent on the optical bandgap, and this originates from the reduced potential difference between the Fermi level at the metal/a-Si : H interface and the electron mobility edge (Ec), with the decrease in the optical bandgap, which reduces the barrier height. Secondly, the barrier height of the Ti/Cu contact is higher than that of the Mo/Al/Mo contact. In particular, an abundance of Ge atoms is found to have been out-diffused towards the surface and to have formed a mixed interfacial layer, having higher work function than that of the Mo/Al/Mo contact. These results provide evidence that the ρc in a-SiGe : H depends on the work function of the contact layer and is potentially useful for improving device performances.