Fabrication,Microstructure And Luminescence Performance Of PbSe Nanocrystalline Films

Nanocrystalline semiconductors with size-tunable band gap and excellent fluorescence performance have been widely applied in the fields such as light-emitting diodes,solar cells and photodetectors.Among various nanocrystalline semiconductors,PbSe has drawn much attention because of its large exciton Bohr radius(46 nm),high dielectric constant and high carrier mobility.As an IV-VI compound,PbSe is a direct band gap semiconductor with the band gap of 0.27 e V of the bulk material at room temperature,which can be adjusted by different element dopants or different preparation techniques.At present,PbSe is widely used in light-emitting diode,infrared detectors,laser transmitters,thermoelectric converters,etc.In most applications,the PbSe material exists in the form of thin film.Hence,the preparation of high-quality PbSe film is the key to expand its application in the photoelectricity field.PbSe nanocrystalline films were prepared by using magnetron sputtering with different sputtering powers and deposition times.The obtained samples were characterized by X-ray diffractometry,field-emission scanning electron microscope,energy dispersive X-ray spectroscopy,X-ray photoelectron spectroscopy,confocal Raman spectroscopy,UV-Vis-NIR spectroscopy and Spectrofluorophotometer.The effects of sputtering power,deposition time and annealing temperature on the crystal quality,surface morphology,chemical composition,optical band gap and luminescence properties of the films were studied.The main research content is divided into three parts:(1)The effects of sputtering power on the microstructure and luminescent properties of PbSe films were studied.The XRD and XPS results show that the crystalline quality of PbSe films increases with increasing sputtering power,and the stoichiometric ratio of Pb/Se tends to 1:1.The optical band gap of PbSe films decreases with the increase of film thickness and grain size.A strong emission peak was observed at 655 nm,and its intensity was closely related to the crystalline quality of PbSe films.(2)The effects of deposition time on the microstructure and luminescence properties of PbSe films were studied.With the increase of deposition time,the shape of PbSe particles firstly changes from near-spherical to rod-like or cotton-like,and then to triangular shape,which is consistent with the change of main growth orientation of PbSe films shown in XRD pattern.The stoichiometric ratio of Pb/Se tends to 1:1 and keeps stable with the increasing deposition time.The long deposition time results in the thick film and large grain size,which leads to the decrease of optical band gap.The variation of emission peak intensity at 655 nm is consistent with the morphology evolution of PbSe thin film.(3)The effects of annealing temperature on the microstructure and luminescence properties of PbSe films were studied.With the increase of annealing temperature,the main growth direction of PbSe film changes from(200)to(111)and then to(220),which is consistent with the change of the morphology of PbSe particles.As the temperature rises,Se element sublimates and the stoichiometric ratio of Pb/Se is out of balance.The grain size increases but the optical band gap decreases with increasing temperature.The intensity of the emission peak at 655 nm decreases with the decrease of the crystal quality of PbSe film.