## 3 Results and Discussion
As shown in Figure 1, low-cost interdigital photodetectors were built on cellulose paper substrate with a MoS\({}_{2}\) active layer synthesized by the microwave-assisted hydrothermal method at different temperatures and times. Figure 5a-c show the current x voltage curves under laser illumination (980 nm) of the photodetectors with a MoS\({}_{2}\) photosensitive  
Figure 4: Raman spectra and micro-Raman mapping of the MoS\({}_{2}\) nanosheets synthetized at 220 \({}^{\circ}\)C with synthesis times of (**a**,**c**) for 05 min and (**b**,**d**) for 120 min. The blue and green mappings represent 1T- and 2H-MoS2 phases in the samples. layer synthesized at 190, 200, and 220 \({}^{\circ}\)C, respectively. The curves are linear and symmetric for the small bias voltage, indicating a ohmic-like contact as observed for the single-layer MoS\({}_{2}\) phototransistor synthesized using the CVD technique [54], or by photodetector built with a multilayer MoS\({}_{2}\) synthesized by the conventional hydrothermal method, using in this case Ag NPs (nanoparticles) as contact [28]. The small bandgap energy of the multilayer MoS\({}_{2}\) may generate a very small Schottky barrier between Ag NPs electrodes and MoS\({}_{2}\). After illumination, carriers are injected into the small conduction band of the multilayer MoS\({}_{2}\) generating photocurrent. The photocurrent increase can be associated with a bias voltage through to the reduction of the carrier transit time (\(\tau_{\text{transit}}=\text{l}^{2}/\upmu\text{V}\)), where l is the length of the channel, \(\upmu\) is the carrier mobility, and V the bias potential [22]. Figure 5: Characterization of infrared photosensors produced with MoS\({}_{2}\) samples grown directly on paper substrates at different times, being: (**a**) kV of samples synthesized at 190 \({}^{\circ}\)C, (**b**) kV of samples synthesized at 200 \({}^{\circ}\)C, (**c**) kV of samples synthesized at 220 \({}^{\circ}\)C, (**d**) lxt of samples synthesized at 190 \({}^{\circ}\)C, (**e**) lxt of samples synthesized at 200 \({}^{\circ}\)C, and (**f**) lxt of samples synthesized at 220 \({}^{\circ}\)C. The lxt measurements were performed with a bias voltage of 4 V, lighting cycles lasting 40 s and power of 20 mW. The curves in Figure 5b,c, for longer synthesis times, present a strong increase in the current x bias voltage (with a non-linear behavior) for bias voltages higher than \(\sim\)2V. This non-linearity in the IxV curve is less intense in the samples synthesized at lower temperature, 190 \({}^{\circ}\)C--Figure 5a, and in the samples with shorter synthesis times for the synthesis temperatures of 200 and 220 \({}^{\circ}\)C, possibly due to the smaller amount of MoS2 material. Figure 5d-f show that there is an increase in both the dark current and the photocurrent, a result that goes according to the discussion held for Figure 5a-c. The increase in the dark current with synthesis time can be associated with the presence of the metallic phase and trap states. To evaluate the infrared photosensors, figures of merit Responsivity (R) and Specific Detectivity (D\({}^{*}\)) were used, which can be calculated using the equations \(R\) = (\(I_{on}\)-\(I_{op}\))/P and \(D^{*}\) = \(R\)/\(\surd\)((2 el_{op}\))/A). Here, I\({}_{\rm{on}}\) is the generated photocurrent in the device under illumination, \(I_{off}\) is the dark current, P is the incident light power on the effective area of the device, \(e\) is the elementary charge and \(A\) is the effective surface area. Figure 6 shows that R and D* values increase with increasing of the synthesis time for three synthesis temperatures and for a bias voltage of 4V. The device built with a sample synthesized at 200 \({}^{\circ}\)C for 120 min has the highest value for both D\({}^{*}\) and R. There is also a big increase of these values for synthesis time longer than 60 min (see yellow curve).