A Research Of Effect Of Buffer Layer On The Growth And Photovoltaic Properties Of PZT/GaAs Heterostructure

The ferroelectric oxide material of the perovskite structure?ABO₃?has attracted wide attention due to its excellent photovoltaic voltage phenomenon.The physical and chemical properties of ABO₃ ferroelectric oxides are relatively stable and can be integrated with common photovoltaic semiconductors by utilizing existing semiconductor process technology,combining high absorption of visible light of direct bandgap photovoltaic semiconductors with high photo-generated voltage of perovskite ferroelectric oxides to form a new type of composite thin film solar cell.However,due to lattice mismatch and interface diffusion,the performance of the heterostructure may be limited.This paper selects the typical perovskite ferroelectric oxide Pb(Zr_0.52Ti_0.48)O₃ as the research object,combines it with the third generation narrow bandgap semiconductor GaAs.In order to improve the crystalline quality and electrical properties of the epitaxial PZT ferroelectric thin films and improve the photoelectric conversion efficiency of the heterostructure,we introduce the composite buffer layers SrTiO₃/TiO₂.The main contents are as follows:1.The composite buffer layers TiO₂ and STO were fabricated on GaAs substrate by laser molecular beam epitaxy.The RHEED observed diffraction patterns were used to analyze and compare the crystallization conditions of buffer layers at different temperatures.Under the premise of ensuring good crystallinity,in order to reduce the interface diffusion problems caused by high temperature,400°C was chosen as the temperature for TiO₂ growth,550°as the deposition temperature of the STO film,TiO₂?110?and STO?110?with good crystal quality were obtained,respectively.2.PZT thin films were grown on TiO₂ and STO buffered GaAs substrates by using pulsed laser deposition system.The effects of oxygen partial pressure and substrate temperature on the growth of PZT thin films were investigated by XRD,AFM,leakage current measurements and so on.The test results show that the sample grown at 550°C and oxygen partial pressure of 15 Pa is optimal with a?101?single orientation.The PZT thin films were grown directly on the GaAs substrate without using a buffer layer.According to the XRD test,the PZT is not crystallized or has multiple crystal orientations when the buffer layer is absent,and the AFM test shows that the surface morphology is rough.The ferroelectric test results show that the ferroelectric polarization intensity of the sample with the composite buffer layer STO/TiO₂ is about 6 times larger than that of the sample without the buffer layer,and the hysteresis loop symmetry is better.3.Photovoltaic test results show that the photogenerated current and photogenerated voltage of the samples with the composite buffer layer are generally larger than those of the samples without the buffer layer.When the buffer layer was used,there was a photocurrent of 11.01 mA/cm² and an open circuit voltage of 0.22 V under simulated sunlight,but much less than the two values when the buffer layer was not used.For the samples obtained under the optimal growth conditions,the photocurrents were measured after different polarizations.The results of comparison of the measurement results show that the photocurrent of the positive polarization mode is the largest,and the value is 38.7mA/cm².Further measure the change of the photovoltaic effect with the light intensity of the positively poled sample.It is found that the photocurrent and the photovoltage increase with the light intensity in a certain range,and approach the saturation when the light intensity reaches about 150 mW/cm².