Study On MgZnO Based Heterogeneous Semiconductor Ultraviolet Photodetectors

With the expansion of the spectrum application range and the rapid development of photoelectric detection technology,ultraviolet(UV)detection technology has been widely used in the military fields of various countries,human medical health,and global environmental monitoring.The research and development of high-sensitivity,low-noise high-performance ultraviolet photodetectors have become the focus and hotspot in the field of photodetection.With the continuous deepening of semiconductor materials and device manufacturing processes,the emergence of wide band-gap semiconductor materials provides new impetus for this research.Wide band-gap materials have frequency band selectivity,which can effectively shield visible and infrared light to avoid the introduction of filter equipments.Moreover,a variety of metal oxide semiconductor materials have been widely used as photosensitive materials for UV photodetectors due to their stable properties,low cost,diverse preparation processes,and properties.MgZnO is an oxide semiconductor material with a wide band gap modulation range.By changing the content of magnesium,its optical band gap can be significantly adjusted from 3.37 e V to 7.8 e V.It can be used for solar-blind or visible-blind UV photodetectors with different cut-off wavelengths.In addition,due to its strong radiation resistance,low defect density,environmental friendliness,and stable chemical properties,it has received special attention in the field of UV detection.However,the high resistivity,low carrier mobility,and many defects of MgZnO thin film materials have led to outstanding performance shortcomings based on a single MgZnO thin film device.With the development of science and technology,the research,development and application of UV photodetectors with higher response,lower dark current and faster response/recovery time is a more promising optoelectronic project.Therefore,in order to solve the above problems,it is proved by experiment and theory that the preparation of heterogeneous composite materials to construct heterostructure is a simple and extremely effective method.In this work,heterogeneous composites and devices based on MgZnO were fabricated.The overall performance of devices based on single material were optimized by combining the advantages of two materials and different working mechanisms of multiple heterostructures.The following research works were carried out:In Chapter 2,MgZnO/Cu₂O heterogeneous composite films UV photodetectors based on the PN heterostructure were designed and fabricated.Compared with devices based on single material,MgZnO/Cu₂O heterogeneous composite films devices have shown a certain degree of improvement in many aspects of performance.In dark,a depletion region will be formed near the PN heterojunction,the majority of carriers in the composite film material are greatly depleted and the concentration is reduced,thus the device exhibits a higher resistance state,thereby reducing dark current.Under UV illumination,the photogenerated carriers are effectively separated and accumulated in large quantities near the PN heterojunction.So as to offset the previous depletion effect,at this time the device returns to a low resistance state.At the bias of 5 V,the peak spectral response is increased by 4 times.In Chapter 3,MgZnO/ZnS heterogeneous composite films UV photodetectors based on the type-? heterostructure were designed and fabricated.By introducingZnS as the interface modification layer between the Au interdigital electrode and the MgZnO film,a thin space charge region with opposite directions can be formed on the basis of the original built-in electric field.The original Schottky barrier height is reduced to promote carrier transport,thereby improving the photocurrent of the device.In addition,MgZnO and ZnS can form the type-? heterostructure at the contact interface.Under UV illumination,the type-? heterostructure can promote carrier transport and greatly reduce the probability of recombination,thereby prolonging carrier lifetime and significantly improving the performance parameters of the device.In dark,the depletion near the heterostructure causes the majority of carriers in the composite film material to be depleted in a large amount,so that the dark current of the device can be effectively suppressed.Compared with devices based on single MgZnO film,the optimized device exhibits an ultrahigh photo-to-dark current ratio(up to 2.3×10⁵),an increased peak spectral response of 900 A/W at a wavelength of 285 nm,and a remarkable detection sensitivity of 1.27×10¹⁵Jones.In this thesis,a series of MgZnO heterogeneous composite film materials based on the heterostructure were studied,which is proved that the heterostructure can significantly improve the carrier transport,thereby comprehensively improving the performance of the device.This thesis opens up a broader research field for the selection of heterogeneous composite materials,the design of heterostructure and the analysis of device working mechanism of the single wide band-gap oxide semiconductor UV photodetector.