In-Substrate Imaging of Diamond–hBN FET Current via Wide-Field Quantum Diamond Microscopy

We report wide-field magnetic imaging of current flow in a hydrogen-terminated diamond FET incorporating a hexagonal boron nitride (hBN) flake as the gate dielectric. The hydrogen termination induces a two-dimensional hole channel, while an ensemble of near-surface nitrogen-vacancy (NV) centers (~10–20 nm below the surface) enables magnetic field mapping of current flow with sub-micron spatial resolution. Electrical characterization was carried out by sweeping the drain–source bias (V_ds = 0 to –15 V) for various gate voltages (V_gs = +3 to –9 V), followed by Nitrogen Vacancy (NV) based magnetic imaging at fixed drain biases. The reconstructed magnetic field maps reveal spatial current distribution across the source–drain channel and through the hBN/diamond interface. During optically detected magnetic resonance measurements, a laser-induced modulation of drain current (~600–900 μA) synchronized with laser excitation was observed, suggesting photoinduced carrier excitation at the interface. These results establish a platform for imaging dynamic charge transport in diamond–2D dielectric field effect devices.