Research On The Photoconductivity Characteristics Of PtSe₂ And SnS₂/Ag₂S Heterojunction Photodetectors

Photodetectors based on two-dimensional materials（TDM）have attracted the attention of many researchers due to their unique structure,excellent electronic and optoelectronic properties.These TDMs include graphene,black phosphorus,transition metal chalcogenides（TMDCs）,group IV metal chalcogenide,and insulating hexagonal boron nitride（h BN）.Up to now,hundreds of articles on TDM based photodetectors have been reported.When some TDMs are used as photosensitive materials for photodetectors,their photoconductivity characteristics may change due to changes in layer thickness,which provides the possibility for preparing photodetectors with negative photoconductivity characteristics.Since the discovery of Graphene by researchers in2004,research on TDM has never been interrupted and has steadily developed in the following decades.As an important type of optoelectronic device,TDM based photodetectors are not only closely related to people’s daily lives,such as smart homes;At the same time,it plays an irreplaceable role in emerging industries such as medical imaging,optical communication,environmental and security monitoring,and optoelectronic integrated circuits.Platinum selenide（PtSe2）is a new transition metal chalcogenide Metal Dichalcogenides（TMDCs）,which was first discovered by Li Linfei and Wang Yeliang’s research team in 2015,quickly aroused great interest among researchers.Like other TDMs,PtSe2 has excellent material properties,but also has its own uniqueness.The photodetector made of it as photosensitive material has achieved wide spectral response from UV-Visible to near-infrared band,and its low cost and better stability of the device have increased its research value.In addition,PtSe2 has a bandgap function related to the layer thickness,which makes its performance highlight different photoconductivity characteristics due to the different layer thickness,which further expands the application of PtSe2 in the field of optoelectronic devices.Selenium disulfide（SnS2）is a metal chalcogenide.SnS2 has a large band gap that can be easily adjusted.At the same time,the stability of the material itself is particularly good.It can maintain good performance when applying a large voltage or temperature.At the same time,the reserve of Sn element on the earth is sufficient,which also reduces its cost to a certain extent,and it is a non-polluting material to the environment,which further expands its application field.The main research contents of this paper are as follows:1.Obtained a wide spectrum PtSe2 photodetector with positive photoconductivity（PPC）and negative photoconductivity（NPC）characteristics at normal atmospheric pressure and room temperature.When analyzing the photoconductivity mechanism of the device,we found that due to the desorption of oxygen（O）or water（H2O）molecules molecules from the PtSe2 surface,NPC became stronger and stronger with the increase of light intensity at the same gate voltage.At high gate voltage,due to the"light gating"effect,the NPC of the device was dominant.At the same time,as the light intensity continues to increase,the desorption of O or H2O molecules reaches the peak,and the photovoltaic effect gradually dominates.At this time,the device shows PPC.To sum up,we conclude that the photoconductivity mechanism in PtSe2 devices is the result of the joint action of current change caused by PPC（（35）I_{p c}）,current change caused by NPC(（35）I_{de s})and current change caused by"optical gating"effect(（35）I_{ga t}).At the same time,we also calculated the photoelectric performance of PtSe2 device.Under the irradiation of 532 nm,808 nm and 405 nm laser,when VG=4 V,the responsivity（R）of PtSe2 device reached 0.14 A/W,0.63 A/W and 0.086A/W respectively;Specific detection rate（D*）reached 4.34×10⁸ Jones、1.95×10⁹ Jones and 2.4×10⁸ Jones,respectively。When VG=-2.4 V,the R of PtSe2 device reaches 0.525 A/W,0.34 A/W and 0.087 A/W,and D*reaches 1.84×10⁹ Jones、1.06×10⁹ Jones and 2.19×10⁸ Jones.2.Designed a SnS2/Ag2S heterojunction photodetectors by stacking SnS2 and Ag2S on the h BN film.In this device,the photogenerated electrons in the SnS2 conduction band（CB）are excited and transferred to Ag2S,and the electrons in the depletion region diffuse to Ag2S.The transferred electrons combine with the photogenerated holes in the valence band（VB）of Ag2S,thus extending the carrier lifetime of SnS2.Under 405 nm laser,R is 4.52 A/W,D*is 3.53×10¹¹Jones,the rise/fall time in a cycle is 37/50 ms.The photoelectric current of SnS2/Ag2S heterojunction photodetector is about one order of magnitude higher than that of SnS2photodetector with single photosensitive material,and several times higher than that of Ag2S photodetector with single photosensitive material.