Optical devices such as displays, LEDs, lasers, solar cells, and optical sensors appear complex, but the key driving principle is the process of converting electrical and optical signals inside a material. For example, when the current injected by the electrode reaches the PN-junction through the layered hetero-thin material, it is possible to think of light emission as electrons and holes merge. When these individual processes are greatly improved or replaced by mechanisms with entirely new properties, innovative optical elements are developed. Our laboratory pays attention to low-dimensional nano-materials that show excellent and unique optical properties, and is an ultra-fast laser analysis method that can observe electron behavior in real time step by step. I am exploring the mechanism.
Very good physical properties have been reported that cannot be seen in 3D materials with 2D nanomaterials of atomic thickness, including graphene. Transition Metal Dichalcogenides is composed of three atomic layers and is a semiconductor thin film.Compared with a general semiconductor thin film, transition metal dichalcogenides has more than 100 times better light absorption / emission characteristics and more than 10 times better electron-hole characteristics. It has a pair-preserving property, and can record '0' and '1' information by light depending on the polarization. In addition, there are surprising predictions that, like electron-hole pair high-temperature superconductors, they can flow without resistance above liquid nitrogen temperature. This is due to both phenomena that are displayed when electrons are confined in a semiconductor with a thickness as small as an atomic size. It is still in the early stages of research, but understanding the underlying mechanism and applying it to optical devices I hope there will be a huge spill over to the information / communications, energy and life / environment related industries.
Our lab manufactures various 2D nanomaterials and artificial heterostructures through mechanical peeling and polymer-based dry lamination. Unlike synthesized 2D nanomaterials, the crystal quality is very high at ultra-high purity level, and the crystal structure can be precisely controlled at the atomic level, so that the best material can be obtained for studying quantum phenomena. Atomic thickness 2D nanomaterials are laminated with van der Waals bonds, so the lamination angle is free and there is no restriction of lattice mismatch, making it possible to create new artificial hetero 2D materials that cannot be made of covalent bond materials. In addition, we are manufacturing LEDs, lasers, solar cells, photosensors, and field effect transistors through the nano-fab process to see how the material's excellent optical properties can be expressed and controlled in the form of real devices.
In order to understand the mechanism of optical properties, it is necessary to experimentally observe the process of electrons interacting with light and transferring charge and energy inside the material. However, the atoms inside the material vibrate at ~ 1000 femtoseconds (10-15 seconds) cycles, and the electrons even change their state of motion at an unimaginable level at even ~ 10 femtoseconds. For this reason, it is very difficult to confirm the process of converting electrical signals and optical signals in optical elements by simple measurement. In our laboratory, we can measure the behavior of electrons in real time with a powerful experimental method called ultra-fast laser analysis technique. Femtosecond-level ultra-fast laser pulses enable instantaneous capture of electron flow as well as atomic vibration. In addition, the laser wavelength can be freely controlled to infrared rays, visible rays, and ultraviolet rays to accurately analyze the charge and energy accumulated or escaped from the material when interacting with light based on the optimized wavelength.