## 3 Results and Discussion
The decrease in the R value obtained in the sample synthesized at 220 \({}^{\circ}\)C for 120 min, when compared to the sample synthesized at 200 \({}^{\circ}\)C for 120 min, may be attributed to the degradation of the cellulose paper. Therefore, the experimental data show that the temperature of 200 \({}^{\circ}\)C and time of 120 min were the best conditions for the production of near infrared photodetectors based on MoS2 active layer grown directly on cellulose paper substrates by the microwave-assisted hydrothermal method. This R value is above the value reported in the literature for photodetectors with active MoS2 layer produced by the hydrothermal method with the same structure. [PERSON] et al. [55] for example, obtained the maximum R value of 23.8 \(\mu\)A/W for excitation at 635 nm, and [PERSON] et al. [28] obtained the R value of 60 \(\mu\)A/W for excitation at 554 nm. It is important to note that temperatures above 200 \({}^{\circ}\)C have generally been used in the literature for synthesis of MoS2, or heat treatments have been made after the synthesis to increase the fraction of phase 2H over phase 1T. At 200 \({}^{\circ}\)C (as in this work), we still have a large proportion of the 1T phase when compared with samples synthesized by the conventional method followed by heat treatment [13; 28]. Therefore, we believe that the  
Figure 6: The Responsivity (**a**) and Detectivity (**b**) according to the synthesis time, for samples synthesized with temperatures of 190 \({}^{\circ}\)C (red triangles), 200 \({}^{\circ}\)C (yellow circles) and 220 \({}^{\circ}\)C (blue squares). Responsivity was measured with a laser power of 20 mW. Graph’s inset shows the external quantum efficiency (EQE) values as a function of time and synthesis temperatures of the MoS2 photoactive layer. increase in the 1T/2H interface, caused by the simultaneous and continuous formation of the metallic phase and its conversion to the semiconductor phase, and the consequent increase in the mobility of carriers in the sample, is of great importance to obtain high values of responsivity in MoS\({}_{2}\) photodetectors. The interface between the paper substrate and the MoS\({}_{2}\) layer may be another important characteristic for devices, once it can be a source of trap states [54] and temperature and time synthesis had a greater effect on the photoconductivity. Thus, the quick increase of the photocurrent to bias voltage (>2 V), as observed in Figure 5, can be associated with the detrapping charge from trap states. It is known that photogain in photoconductors increases as carrier lifetime and decreases as transit time \(G\) = \(\tau_{life}\)/\(\tau_{transit}\)[22]. Figure 6 shows the external quantum efficiency (EQE) of the devices. EQE was obtained by using \(EQE(\%)=Rlc/(\lambda e)x100\). Here, R is the responsivity, \(h\) is the [PERSON]'s constant, \(c\) is the speed of light in vacuum, \(e\) is the elementary charge, and \(\lambda\) is the wavelength of the excitation light. As can be seen, the EQE increases as the time synthesis increases, similar to R and D\({}^{\bullet}\). The device built from MoS\({}_{2}\), synthesized at 200 \({}^{\circ}\)C for 120 min, presents an EQE value of 26%. The MoS\({}_{2}\) photodetector has a relatively high R value, compared to other similar devices based on MoS\({}_{2}\) synthesized by the hydrothermal method. The rise and the decay response time has high values (\(\tau_{rise}\) = 3.7 s e \(\tau_{decay}\) = 4.7 s) which may be associated with the high concentration of the metallic phase in MoS\({}_{2}\) and trap states in the MoS\({}_{2}\) and/or paper/MoS\({}_{2}\) interface. In comparison, the HfO\({}_{2}\)-gated single-layer MoS\({}_{2}\) phototransistors, with high responsivity due to the photogate effect, present a slow response of 0.6-9.0 s. In this case, the slow response time and the high responsivity was induced by the trap states in the MoS\({}_{2}\) or MoS\({}_{2}\)/SiO\({}_{2}\) interface [54] [PERSON] et al.