Shimane University, Fujita-Yoshida Lab.

Shimane University has succeeded in producing nitrogen-doped ZnO nanoparticles by the gas evaporation method, in which zinc is evaporated by arc discharge in reduced-pressure air. These particles realize stable p-type conduction, which has been difficult to achieve with zinc oxide, and it was found that by coating these particles on n-type zinc oxide, light-emitting diodes in the near-ultraviolet region can be produced. The fabrication process of this nanoparticle-coated LED does not require an advanced vacuum process because of the use of oxide, and can be applied in the atmosphere. Also, there is no need to use single crystals, making it possible to realize ultra- low-cost light-emitting diodes. Furthermore, since they emit light in the near-ultraviolet region, they can be combined with phosphors to produce white and RGB light, and are expected to be used in large-area lighting devices and micro-sized display pixels.

Some of the research results were featured in Semiconductor Today news. https://www.semiconductor-today.com/news_items/2024/jul/shimane-240724.shtml

Related patents

Japanese patent No.4072620

Japanese patent No.5277430.

Japanese patent No.6004404, JP201305472, WO2013125719.1.

Japanese patent application, JP2019-110258.

Japanese patent application, JP2020-5112.

Shimane University has developed a MOCVD system for ZnO thin film growth through a JST-funded research project, and succeeded in growing high-quality undoped ZnO single-crystal thin films that are superior to those grown by MBE. Using this equipment, we have succeeded in growing nitrogen-doped MgZnO and fabricating the world's first near-ultraviolet single hetero LED using MOCVD. It is also possible to grow gallium-doped transparent conductive films with low resistivity and high-speed phosphors suitable for low-light detection. These technologies have been commercialized through S-Nanotech Co-Creation, a Shimane University initiated start-up venture, and epitaxial thin films fabricated by MOCVD have been commercialized.

Related Patents

Japanese patent No.3605643.

Japanese patent No.6676372.

Japanese patent No.6948675.

This research uses semiconductor nanoparticle layers instead of semiconductor thin film layers to create layers acting as semiconductor thin films even in various locations (substrate materials and surface morphologies) that cannot be used in conventional semiconductor thin film fabrication techniques. The aim is to apply them to a wide range of fields including solar cells, displays, and sensors. We have already demonstrated n-type and p-type TFT operation using ZnO nanoparticle layers. We are currently aiming to reduce parasitic resistance, and in the process, we discovered that thermal diffusion doping into ZnO nanoparticles is possible. We explore new discoveries by incorporating the potential of nanoparticles into semiconductor device fabrications.

ZnO is a semiconductor that exhibits photocatalytic activity, producing reactive oxygen species from water and oxygen upon light absorption. ZnO is chemically unstable compared to titanium dioxide, which is used as a photocatalyst. However, zinc oxide has excellent dark and visible response properties, making it suitable for antimicrobial and antiviral applications. Our laboratory is the only one in the world that can synthesize p-type and n-type zinc oxide nanoparticles. p-type nanoparticles accumulate electrons on the surface and undergo a reduction reaction, while n-type nanoparticles accumulate holes on the surface and undergo an oxidation reaction. Conventional photocatalysts require the use of a metal support to separate electrons and holes in order to increase efficiency, which increases cost and causes the supported metal to release. By using the properties of semiconductors to control the band bending on the surface through conductivity control, it is possible to separate electrons and holes, thus eliminating the need for a supported metal and providing a highly efficient photocatalyst. Furthermore, the photocatalyst has been confirmed to be effective as an anticancer agent. The antibacterial effect of this photocatalyst is effective even under light-shielded conditions, so the weak effect persists even inside the body, and even if cancer cells are killed, it has been confirmed that it has an excellent effect without toxicity to normal cells. It is also effective against cancer cells that are resistant to conventional anticancer drugs.

Related patents

Japanese patent application JP2023-106792.

Related Papers

Mol Cancer Ther; 19(2) February 2020.

Photonics and metamaterials technologies control light and electromagnetic waves, and acoustic crystals and metamaterials apply these technologies to sound waves. The left photo shows a semiconductor crystal with a nano-sized crystal structure. Changing the atoms that make up the crystal changes the energy state of the electrons, and depending on the size of the band gap energy, which is related to light absorption characteristics, visible light can be transmitted or absorbed. The electron wave is controlled by nano-sized crystals with the wavelength of an electron. Advanced semiconductor crystal growth technology is required to fabricate these materials. In addition, the fabrication of metamaterials that artificially control light waves with properties not found in the natural world requires microfabrication technology at the wavelength of light. In contrast, acoustic crystals and acoustic metamaterials that control sound waves and ultrasonic waves require structures on the order of millimeters to centimeters, so crystals with a controlled band gap for sound waves can be easily fabricated with a 3D printer, as shown in the photo at right. Using these technologies, it is possible to create crystals with negative mass, which is not found in nature, in contrast to the mass law of sound insulating materials (heavy materials are necessary to stop low-frequency sound), making it possible to stop low-frequency noise with light materials. Thus, if we apply the semiconductor and photonics technologies that control electron and light waves to sound waves, it is expected to lead to new industrial applications.