Lasers can transform complex semiconductor properties in a single-step process

A research team has successfully developed a new technology that transforms the conductive properties of semiconductors with just one laser process.

A research team has successfully converted titanium oxide (TiO2), which traditionally functions based on electrons, into a hole-based p-type semiconductor. The LODI (Laser-Induced Oxidation and Doping Integration) technology developed by the research team is attracting attention as a new conversion technology that can perform oxidation and doping at the same time with just one laser irradiation, making conventional complex processes significantly more efficient.

The study was published in the journal Small. The team was led by Professor Hyukjun Kwon from the Department of Electrical Engineering and Computer Science at Kyungbuk University of Science and Technology, Daegu.

Semiconductors are classified into two types (n-type and p-type) based on the main particles that conduct electrical current. In n-type semiconductors, negatively charged electrons (e-) move and cause current to flow, while in p-type semiconductors, holes (h+), which are empty spaces within electrons, move and cause current to flow. Most electronic devices, including smartphones and computers, operate on complementary metal-oxide-semiconductor (CMOS) circuits that take advantage of the properties of both. Therefore, efficient circuit design requires both n-type and p-type implementations.

Titanium oxide (TiO2), on the other hand, has been considered an “ideal semiconductor material” because it is non-toxic, abundant, and thermally and chemically stable. However, its crystal structure is very stable, which limits the movement of holes. Therefore, it acts only as an n-type semiconductor, carrying only electrons (e-). This means that the material exhibits good performance and stability, but can only be used in “half the circuit.”

To address these limitations, the research team developed LODI. This technology is an integrated process that simultaneously performs oxidation and doping with one laser, integrating complex semiconductor manufacturing processes into one step.

When an aluminum oxide (Al2O3) film is placed on top of a titanium (Ti) metal thin film and irradiated with a laser for several seconds, the titanium combines with oxygen to form titanium oxide (TiO2), and aluminum ions diffuse inside. In this process, the balance of electrons is disrupted and holes are created, forming a p-type semiconductor in which holes conduct current instead of electrons.

Converting a titanium oxide semiconductor to p-type requires a complex process that takes several tens of hours, including high-temperature heat treatment and vacuum ion implantation. It also requires expensive equipment and a high vacuum environment, which limits commercialization.

On the other hand, LODI can achieve a similar effect in a few seconds with a single laser, allowing oxidation, doping, and patterning to be performed simultaneously, and is expected to be a next-generation semiconductor manufacturing technology that can significantly reduce process time and cost.

Professor Hyukjun Kwon said, “This research is significant in that it converts titanium oxide semiconductors, which have been mainly used in n-type, to p-type while streamlining the conventional complex process into a single laser process.” “This unique technology that allows us to precisely control the conductivity type of oxide semiconductors will be the foundation for realizing the next generation of highly integrated and reliable devices.”