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 × 108 Jones, 1.95 × 109 Jones, and 2.4 × 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 × 109 Jones 1.06 × 109 Jones, and 2.19 × 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.