Fig. 1. The schematic diagram of the metal-GN-metal structure

Fig. 2. AFM images of two opposite interfaces between graphite nanosheet and Si substrate，the two-step heights between graphene nanosheets and high resistance Si are calculated by the difference of the maximum peak height and minimum peak height，the two-step heights are 148 nm（left picture）and 144 nm（right picture）respectively

Fig. 3. The schematic diagram of Terahertz test system

Fig. 4. （a）The I-V curve of the detector，（b-c）the responsivity of the detector at the source frequency of 0.02-0.04 THz and 0.165-0.173 THz with the bias voltage of 0.1V，respectively，（d）the noise spectrum at the frequency from 250 Hz to 100 kHz with the bias voltage from 0.1 V to 0.01 V

Fig. 5. （a）The waveform of the detector and time constant derivation from the waveform at 0.035 THz with the modulation frequency of 1 kHz，（b）the frequency dependent responses of the detector with different bias voltage（0.01 V，0.02 V，0.05 V and 0.1 V）at the source frequency of 0.035 THz，（c-d）the responsivity of the detector under different bias voltages at the source frequency of 0.035 THz and 0.1673 THz with the modulation frequency of 1 kHz，respectively