Pusan National University Team First in the World to Uncover Picosecond-Scale Current Response Switching

Professor Jihee Kim's Physics Team
Paving the Way for Next-Generation Ultrafast AI Computation and Quantum Information Devices

A research team at Pusan National University has, for the first time in the world, discovered a phenomenon that goes beyond simply switching an electric current on and off: the team observed the reversal of the sign (negative to positive) of the current response at the picosecond scale-one trillionth of a second.

This achievement is expected to open new possibilities for applications in future core technologies such as ultrafast AI computation and quantum information devices.

Pusan National University (President Choi Jaewon) announced on the 25th that Professor Jihee Kim's research team from the Department of Physics has identified a mechanism in which the electric field at a two-dimensional semiconductor-metal van der Waals interface is instantaneously reversed by light, causing the photoconductive signal to switch reversibly. The research results were published in the September 12 issue of the international journal Science Advances.

Professor Jihee Kim. Provided by Pusan National University

Previous studies assumed that the internal electric field at the two-dimensional semiconductor-metal interface was fixed, which limited the ability to control the photoconductive signal with ultrafast precision. To control photoconductive switching, complex external devices such as gate electrodes or gas pressure regulators were required, and the response speed was limited to the nanosecond (one billionth of a second) to microsecond (one millionth of a second) range.

The research team utilized ultrafast photocurrent spectroscopy to observe the process in which the electric field at the MoTe₂/Pt Schottky junction interface is dynamically reversed as charges are photoexcited. Through this, they directly confirmed that the transition from negative photoconductivity (NPC) to positive photoconductivity (PPC) occurs at the picosecond scale (one trillionth of a second).

Based on this phenomenon, the team proposed and implemented a voltage-programmable NPC/PPC photodetector, demonstrating that the switching point can be precisely controlled at the picosecond scale with only a few millivolts of fine voltage. This device can selectively operate in negative or positive photoconductive modes without the need for gate electrodes or external modules, overcoming the structural complexity and high power consumption issues of conventional photodetectors.

Professor Jihee Kim stated, "This research is the first case to demonstrate that current response at a metal-two-dimensional material interface can be reversibly controlled at the picosecond scale through light and interface interactions," adding, "We will continue research to reach the femtosecond time scale, contributing to the development of various next-generation technologies such as ultrafast optical communication, neuromorphic computation, and quantum information devices."