Study On High-temperature Characteristics And Photoelectric Properties Of Nanocrystalline CdSe Thin Film

Visible-light photoresistors have attracted more and more attention due to huge potential in many applications,such as the photoelectric counter,the smoke alarm,especially the solar energy tracking system,compared with the non-tracking method,whose efficiency of photovoltaic power generation is increased by 35%.The visiblelight photoresistor is the core device of photovoltaic automatic tracking system for solar energy,research and design on a high sensitivity,high precision,high controllability,high photoelectric conversion efficiency and small photoresistors is extremely urgent.As a kind of important material for photoresistors,cadmium selenide(CdSe)is a II-VI semiconductor compound material,with a wide band gap of 1.74 eV at 300 K,which matches the visible band of solar spectrum.CdSe has been widely used in optoelectronic devices such as laser devices,solid-state diode and solar cells.In this thesis,visible-light photoresistors based on CdSe nanocrystalline films are systematically studied.The main contents of this thesis are divided into the following sections:1.The CdSe nanocrystalline thin films have been prepared by the vacuum evaporation technique on the substrate of Si(100)under various evaporation currents.The analysis and characterizations of crystallization properties and surface morphology are carried out by X-ray diffraction(XRD),thickness testing instrument,Atomic Force Microscopy(AFM).The results show that the evaporation current has significant influence on the crystalline properties and morphology of CdSe thin films.When the evaporation current is 75 A,the strongest diffraction apex was on the(002)crystal face,which exhibits an obvious growth advantage of the film along the c axis orientation,and the thickness of film is about 160 nm and the grain size is about 40 nm.The sample surface for 75 A is smooth and crack-free with root mean square(RMS)roughness as 5.63 nm,the thin film crystalize relatively well.2.The CdSe fims prepared under the evaporator 75 A were annealed in the vacuum for 3 h,and the annealing temperatures are 523 K,the 673 K,the 723 K and the 773 K,respectively.Under the condition of the vacuum,effects of the different annealing temperatures on the structure properties and surface morphology of samples were studied.The XRD and Scanning electron microscope(SEM)results demonstrate,the ideal annealing temperature is 723 K.3.High-temperature XRD test was carried out on the CdSe nanocrystalline film deposited under the evaporation current at 725 K temperature.The results show that the CdSe nanocrystalline films have high-temperature stability below 1073 K.With the increase of temperature,the lattice constants of CdSe nanocrystalline films,the coefficient of thermal expansion along the c-axis increase gradually,while the dislocation density and strain of CdSe nanocrystalline films decrease.Compared with the block CdSe,due to the special surface effect and the size effect,the temperature characteristics of CdSe nanocrystalline films have changed greatly.4.Visible-light photoresistors of CdSe nanocrystalline films were developed,and the voltage-resistance characteristic,the illuminance-resistance characteristic and the annealing temperature-resistance value was studied.