Controlling transient photocurrents at semiconductor interfaces

Self-powered sensing and energy harvesting applications are looking to leverage transient spike photocurrents — generated under pulsed light at semiconductor interfaces — for their fast response, high peak current density, and broad material compatibility. However, thus far phenomenological theories only partially explain the mechanisms of generating these transient signals.

To better understand transient photocurrent dynamics, Qiu et al. designed a structure that absorbs photons and generates electrons and holes, enabling the quantification of photogenerated carrier density and its spatial distribution under competing junction effects. Their structure consists of a p-n and Schottky back-to-back junction.

“Considering the key role of photogenerated carriers in shaping the quasi-Fermi level and its distribution, thereby affecting carrier transport, we are motivated to start from this most fundamental process to design experiments and construct a direct link between macroscopic transient photocurrent and the quasi-Fermi level,” said author Zhaona Wang.

The group varied the illumination wavelength and the manganese doping concentration in the dual-junction structure, measuring the resulting energy-level shifts. By quantifying the competition between the p-n and Schottky junctions and determining the inflection point at which competition reaches a balance, they achieved precise modulation of net transient photocurrents.

The group next plans to examine how band structure engineering and junction width modulation affect carrier transport probabilities in dual-junction devices.

“This insight is important for on-demand tailoring and dynamic control of the photocurrent polarity inflection point, a key feature for advanced signal processing,” said Wang.

In closing the gap between theoretical modeling and practical scenarios, the group expects to introduce novel functionalities in intelligent optoelectronic systems, like self-powered bipolar sensing and wavelength-selective polarity switching.

Source: “Competition-induced bipolar transient photocurrent as a probe of quasi-Fermi level dynamics,” by Xianchun Qiu, He Huang, Meng Zhu, and Zhaona Wang, Applied Physics Letters (2026). The article can be accessed at https://doi.org/10.1063/5.0323005 .