Semimetallic PtSe2 Phototransistors with Back-to-Back Ohmic Contacts for Low-Power Neuromorphic Vision and Polarization-Selective Detection

The rapid advancement of artificial intelligence has created an urgent demand for energy-efficient neuromorphic vision, positioning phototransistors as a promising platform for next-generation artificial visual synapses. However, conventional phototransistors are limited by interfacial defects─including Schottky barriers and Fermi-level pinning─which cause high power consumption, inhibited carrier transport and degraded synaptic performance, rendering the fabrication of high-quality ohmic contacts a necessity. Here, we report high-performance Au-contacted phototransistors based on high-mobility semimetallic multilayer PtSe2. Its semimetallic nature creates an ultrathin interfacial depletion region for efficient carrier tunneling, realizing a back-to-back dual ohmic contact structure that fully eliminates interfacial parasitic interference. Synaptic responses are thus governed by intrinsic photoconductive and photothermally modulated conductivity effects. Benefiting from this optimal contact design, the semimetallic PtSe2 phototransistor exhibits stable, repeatable synaptic behaviors at an ultralow bias across 20–63.2 °C. Beyond thermally robust synaptic plasticity, the semimetallic PtSe2 phototransistor shows prominent polarization-dependent photoresponse with a polarization ratio of 13.2 under 1550 nm light. In neuromorphic tests, the handwritten digit recognition network retains >89% accuracy under Gaussian noise (σ = 1.2), and the U-Net model achieves high-fidelity reconstruction of partially occluded digits. Featuring wide-temperature stability, ultralow-power operation and excellent polarization sensitivity, the semimetallic PtSe2 phototransistor enables high-performance neuromorphic computing and polarization detection for complex environments.