Study On The Chemical Bath Synthesis And Optical Propertiesof Silicon-based PbS Nanometer Films

In this thesis, a series of the polycrystalline intrinsic and doped Pb S nano-scale films were deposited on p-type Si（100） substrates by low-cost chemical bath deposition using different rapid thermal treatment temperatures(T_rtt), precursor concentrations and complexing agents. The effect of the processing parameters was also intensively studied on the microstructure, optical, and electrical properties. Utilization of XRD and cold-field SEM characterized the microstructure and surface pattern of the films, and utilization of spectrophotometer characterized the optical absorption properties of the films in near-infrared region. The thickness and the electrical resistivity of the films were determined by cross-section SEM images and high resistance tester, respectively. The main findings are listed as follows:（1） The nano-scaled Pb S films have cubic polycrystalline structure before and after the rapid thermal treatment. The grain size of the films is, to some extend, isotropic. The Pb S films tend to be more compact and surface roughness and average grain size of the films first increase and then decrease with increasing the T_rtt. The thickness of the films decreases on a whole. The Tauc equation-fitted optical absorption edges of the films in the near-infrared region, ranging from 0.99 to 1.24 e V, first redshift and then blueshift with T_rtt. The Pb S film at T_rtt = 300 oC has the best crystallization, the widest absorption edge and the best absorption properties in the near-infrared region.（2） In the process of reaction, the precursor concentration has certain effect on the formation of the films. With increasing the concentration of sulphor source, the absorption edge of the films first blueshifts and then redshifts. The film has the best quality and absorption properties at uniform concentrations of lead and sulphor sources. The film has a poor quality without any complexing agent, while when using certain complexing agent（NH₃H₂O, TEA and TSC）, the film tends to be compact, uniform, and smooth and be composed of the particles of different sizes and shapes that change with the utilization of difficult complexing agents. The Pb S film has the biggest thickness of 429.9 nm and wider optical band gap of 1.43 e V when using TEA as complexing agent. The average grain size of the film in the orientation <111> and <200>is very different. The shape of the grain is far from being spherical because of the anisotropy of the crystallite size of Pb S films in different directions. The average particle size of the films gradually increases and the particle shape changes from irregular to regular triangle with increasing the C_m value. The absorption edge of the film first redshifts and blueshifts with the C_m（critical C_m value = 0.2 M）.（3） The intrinsic Pb S and Pb S:Zn²⁺ films are cubic polycrystalline structure and are <200> oriented. With increasing the Zn²⁺ concentration(C_Zn), the average grain size（22 nm⁷4 nm） in the orientation <200> almost first decreases and then increases, while the change trend of that in the orientation <111> is opposite to the orientation <200>. And the particle shape changes from initial irregular to triangle and pyramidlike with C_Zn. The absorption edge of the Pb S:Zn²⁺ films first blueshifts and then redshifts with the C_Zn. The former is attributed to the Burstein-Moss effect and to the increased tensile stress on crystal face（111）, while the latter is to the decreased tensile stress on crystal face（111）. The electrical resistivity of the films first decreases from 1.31×105 W×cm to 1.0×102 W×cm, and then slightly increases with the C_Zn.（4） Polycrystalline Pb S:Al³⁺films with different optical band gaps were deposited by modifying the Al³⁺concentration. The absorption edge of the films varies in the range of 1.18 to 2.12 e V, resulting into the change of the absorption from near-infrared to visible region. The doping of Al³⁺can not only modify the optical band gap of the films, but also change the electrical resistivity, thus improving the electrical conductivity of the films. The co-doping of alkali metal ions to Pb S films has no clear effect on the modify of the optical band gap of the base material, however, can change the optical band gap in the limited region.