Controlled Growth Of Polychalcogenide Single Crystals And Their Photodetection Properties

Infrared photodetectors,which can convert infrared lights into electrical signals,are of great significance in both military and civil fields.The materials that can be used for infrared photodetections should be narrow bandgap semiconductor materials.In addition to the ?-? or ?-? compounds that have been widely studied,many ternary or poly-chalcogenides also have bandgaps that match the wavelength of infrared lights.In this thesis,poly-chalcogenides which have not been deeply studied are focused on.In order to study the intrinsic photoelectric properties of these materials,single crystals of these materials are prepared and photoconductive photodetectors are fabricated with these as-prepared single crystals.The main contents of this paper are as follows:1.Weak light photodetection is considerably potential in both theoretical and technical aspects while it would be a key issue to explore new candidate material for practical application in view of high reliabity and durability of the devices under ambient conditions.In this work,Ag2HgS2 single crystal rods(SCRs)with length up to 1.2 cm and width ranging from 10 to 200 ?m have been successfully fabricated in pure phase via facilely solvothermal process at 200? for 24 h for the first time.The Ag2HgS2 SCRs are technically investigated,and the study reveals that they are in high quality over the determination of their crystal structure,morphology and optical properties.Density functional theory(DFT)calculations have been carried out to explore more reliable details on the band structure of bulk Ag2HgS2.Meanwhile,a series of photodetectors based on the individual Ag2HgS2 SCRs have been fabricated,and they convey sensitive responses to a 0.170 ?W cm-2 weak light and unanimous responses to incident lights with different wavelengths from 254 to 980 nm.In addition,the devices behave excellent detecting performances without any obvious slump after the Ag2HgS2 SCRs exposed in air over 18 months.2.Sulfoiodide crystal possesses promising properties and functionalities that would be used for technical applications in many areas.Lead sulfoiodide(Pb5S2I6)single crystal with high quality has been successfully synthesized via a rapid hydrothermal process at temperature as low as 160? for 10 h with the assistance of acid media,and an individual Pb5S2I6 crystal based photodetector is first constructed on SiO2/Si substrate.The first-principles density functional theory(DFT)calculations are performed and the photoresponse performance of Pb5S2I6 crystal is studied for the first time.The photodetector displays a remarkable response to visible light with an on-off ratio up to 650,a responsivity of 0.567 mA W-1,a detectivity of 2.69 × 109 Jones,a noise equivalent power of 4-08 × 10-13 W Hz-1/2 and a fast rise/decay time of less than 0.2 s.3.BiTeI and SbTeI are also M-VIA-VIIA compounds,which are in the same class to Pb5S2I6.The crystals of these two materials were synthesized by solid phase method.After confirming the band gap of BiTeI which can be stable in air by DFT calculation,both heterojunction type and photoconductive type of BiTeI photodetectors are fabricated based on the BiTeI solution dispersed in anhydrous ethanol,and tested their photodetection performances for the first time.The results showed that the BiTeI crystals with high conductivity could response to visible light and near-infrared light and its photodetection performances were excellent and stable.The on-off ratio of the heterojunction BiTeI photodetector could reach 677 at 0 V bias,while the device had a responsivity of 31.8 mA W-1,a detectivity of 3.46 × 109 Jones and a noise equivalent power of 5.79 × 10-11 W Hz-1/2 at 2 V bias and 50 mW cm-2 incident light.The device also showed an ultrafast response time of 31 ?s.All the above results had made up for the blank of the current research on the photodetection properties of BiTeI,and proposed a new photoelectric conversion material with good optical properties in both visible and near infrared band.