Geometrical Tailoring of Shockley-Ramo Bipolar Photocurrent in Self-powered GaAs Nanodevices

TL;DR

This paper demonstrates how nanoscale geometric engineering in GaAs nanodevices enables reversible bipolar photocurrent responses by exploiting reversible electron-hole asymmetry, advancing self-powered optoelectronic device capabilities.

Contribution

It introduces the first demonstration of bipolar Shockley-Ramo photocurrent in GaAs nanostructures through geometric control of carrier dynamics.

Findings

Bipolar SR response achieved in GaAs nanoconstrictions.

Carrier dynamics modulated by geometry enable polarity control.

Polarity reversal driven by excitation-dependent intervalley scattering.

Abstract

Bipolar photoresponse - where photocurrent polarity reverses with excitation wavelength, gate voltage, or other conditions - is essential for optical logic, neuromorphic computing, and imaging. Unlike unipolar responses, bipolar behavior enables direct binary encoding and enhanced photodetection contrast. However, in conventional photoconductive or photovoltaic systems, the simultaneous and opposite-directional transport of electrons and holes often suppresses polarity switching. Recent self-powered Shockley-Ramo (SR) photoresponse in gapless materials also show only unipolar signals due to strong, irreversible electron-hole asymmetry. Here, we demonstrate for the first-time bipolar SR photoresponse in GaAs nanoconstriction devices by exploiting reversible electron-hole asymmetry. The longer carrier lifetimes in GaAs enable sub-diffusion-length control of carrier dynamics through geometry. By tuning photocarrier dynamics near the nanoconstriction for both majority electrons and minority holes, we modulate the SR response to exhibit dual polarities. At low excitation, photoelectrons dominate; as excitation increases, intervalley scattering populates higher-energy L-valleys, reducing electron contribution and leading to polarity reversal driven by the growing dominance of photoexcited holes. These results, supported by SR theory, show that nanoscale geometric engineering, together with the reversible electron-hole asymmetry, enables self-powered bipolar photocurrent responses, offering new routes toward advanced optoelectronic devices.