PtSe2 Field-Effect Phototransistor with Positive and Negative Photoconductivity

Platinum diselenide (PtSe2) has been exploited for visible and infrared photodetectors due to its tunable electrical and photoelectric properties determined by a layer-dependent band gap. We investigated the photoconductive mechanism of the few layer (3 nm) PtSe2 field-effect phototransistor (FEPT) under illumination of visible and infrared lasers. The few-layer PtSe2 FEPT shows ambipolar characteristics modulated by a gate voltage with a mobility of 1496.7 cm2 v-1 s-1 (electron) and 1410 cm2 v-1 s-1 (hole) at VDS = 0.16 V. Both positive photoconductivity (PPC) and negative photoconductivity (NPC) were observed in the PtSe2 photodetector. The responsivity (R) of the device at VG = 4 V was 0.14 A/W, 0.63 A/W, and 0.086 A/W, and the specific detectivity (D*) was 4.34 x 108 Jones, 1.95 x 109 Jones, and 2.4 x 108 Jones under 532, 808, and 405 nm laser irradiation, respectively. The R of the device at VG = -2.4 V was 0.525 A/W, 0.34 A/W, and 0.087 A/W, and theD* was 1.84 x 109 Jones 1.06 x 109 Jones, and 2.19 x 108 Jones. The change of the photoconductivity is attributed to a combination of three mechanisms: (1) photoinduced desorption of oxygen molecules from the surface, which is related to the NPC; (2) the photoinduced carriers, which leads to PPC; and (3) the photogating effects related to the photoinduced electrons in the interface of PtSe2/SiO2. NPC dominates in the device at a high gate voltage due to the photogating effect. Through the study of the P/NPC mechanism in PtSe2, understanding of the photoconductive mechanism in the field of photoelectric detection is further deepened.

Automated summary

By investigating the photoconductive mechanism of a few-layer PtSe2 field-effect phototransistor (FEPT), we found that both positive and negative photoconductivity can be observed. The changes in photoconductivity are attributed to the photoinduced desorption of oxygen molecules, photoinduced carriers, and the photogating effects caused by photoinduced electrons at the PtSe2/SiO2 interface.