*3.2. NEP*

NEP was equal to the noise spectral density (NSD) divided by the responsivity. In addition, the NSD was obtained by measuring noise voltages using a dynamic signal analyzer as detectors were biased at 2.5 V [36]. As the proposed detector operated at 0.91 THz with a modulation frequency of 2 Hz, it obtained an NEP of 1.28 μW/Hz0.5. Besides, as the detector operated at 2.58 THz and 4.2 THz, it almost reached saturation

at a modulation frequency of 0.5 Hz, thus corresponding NEPs were 2.19 μW/Hz0.5 and 2.37 μW/Hz0.5, respectively.
