Preparation And Characteristic Of ZnO/Si Heterojunction

Band offset and interface state of the semiconductor heterostructures are the two most critical factors in performance, but also the most essential physical roots. In this paper, the ZnO/Si heterojunction electrical properties were studied from two aspects of the interface state and band offset.In this work, in order to reveal the conduction mechanism of ZnO/Si heterojunction, the voltage-current and capacitance–voltage characteristics of the ZnO/p-Si heterojunction in ideal conditions are investigated base on the p-n junction diffusing model and the Anderson diffusing model, the effects of doping concentration, working temperature and band offset on the voltage-current and capacitance–voltage characteristics are analyzed. According to the p-n junction model of Shockley, the relationship between the equilibrium carrier concentrations for n-type and p-type semiconductors on the edges of the depletion region for an n-ZnO/p-Si heterojunction solar cell is analyzed. The relationship between the photovoltage and built-in voltage for n- ZnO/p-Si heterojunction solar cell is discussed, and the expression of the total I-V characteristic is given. Using n-ZnO/p-crystalline Si heterojunction structure may improve photoelectric conversion efficiency of solar cells, especially in light-gathering solar cells. The voltage-current and capacitance–voltage characteristics of the ZnO/n-Si heterojunction in ideal conditions are investigated. Because of the difference of the Fermi level relative position, the ZnO/n-Si heterojunction shows two different rectifying behaviors.Based on detailed balance theory and considered the barriers at interface of heterojunction which result from the band offset and block photon-generated carriers transport, a photoelectric conversion model for n-ZnO/p-Si heterojunction solar cells is established. The problem of the limit efficiency of heterojunction solar cells can not be calculated using the detailed balance theory is solved. A method to realize the I-V characteristics of the n-ZnO/p- Si heterojunction solar cells under the illumination and the limit conversion efficiency of n-ZnO/p-Si heterojunction solar cells is proposed in this work. It is shown that a theoretical efficiency limit of 29% can be achieved for n-ZnO/p-Si heterojunction solar cells under AM1.5 illumination. Because of the ZnO / Si heterojunction interface lattice mismatch, a large number of interface states are formed. The CuSCN and CuI are molecular crystals, and soft material properties. Although the CuI and CuSCN have different coefficients of thermal expansion, compare with the Si and ZnO, respectively, but when the heterojunction is made, it do not have a greater stress, not a large number of dislocations, and defects formation at the interface and not produce a large number of interface states. In order to understand the effect of passivated defects with the CuI and CuSCN thin interlayer in an even better fashion, the p-CuI/n-ZnO, p-CuI/n-Si and p-CuSCN/n-Si heterojunction has been prepared by chemical method. The CuI and CuSCN films are prepared by the successive ionic layer adsorption and reaction (SILAR) technique and the ZnO film is prepared by the chemical bath deposition (CBD). The p-CuI/n-ZnO heterojunction shows a good rectifying behavior with a rectification ratio～600 at 3 V. The p-CuI/n-Si and p-CuSCN/n-Si heterojunction show a good rectifying behavior and a good photoelectrical effect.The n-ZnO/Si heterojunction prepared by magnetron sputtering shows a good rectifying behavior and a good photoelectrical effect. The high density interfacial state at the ZnO/Si interface is reduced by the CuI and CuSCN thin interlayer between the Si substrate and the ZnO film. The effect of passivated defects with CuI film is better. By a comparison of the n-ZnO/p-Si heterojunction properties, the n-ZnO/CuI/n-Si and n-ZnO/CuSN/n-Si heterojunction show improved electrical properties, with a fairly low leakage current and high rectification ratio. But for n-ZnO/n-Si heterojunction, the electrical properties are not improved by inserting CuI and CuSCN thin interlayer.