Figure 2

Schematics of the experimental set-up. The optical excitation using a green laser, the microwave(μw) control and the lock-in detection are depicted. The optical excitation is switch on and off using an Acousto Optic Modulator (AOM). The green laser beam is focused to a spot of \({\sim}(10 \times 10 )~\mu \mathrm{m}^{2}\) size. A Dichroic Beam Splitter (DBS) is used to separate the optical path of the green excitation and of the red photoluminescence (PL). The 96% of the PL is then sent to a photodiode (PD), the remaining 4% is sent single-photon avalanche detector(SPAD). In the inset a drawing of the sample is shown. The sensing layer has a thickness of 15 nm and a is localized at depth of 10 nm below the surface