| In As/Ga Sb type-? superlattice has many natural advantages in the preparation of infrared detectors due to its unique energy band structure compared with other infrared detection materials,and is considered to be the new generation of high-performance infrared focal plane preferred material system.With the development of epitaxial growth technology,superlattice focal plane devices of multiple detection wavelength ranges have been realized internationally.However,the actual performance of In As/Ga Sb type ? superlattice detectors still has some gaps with theoretical expectations,especially the quantum efficiency of superlattice detectors is only about half of the quantum efficiency of mercury cadmium telluride?MCT?detectors.Quantum efficiency is affected by two mechanisms,light absorption and photoelectric conversion,so full light absorption is a prerequisite for high quantum efficiency.Thin epitaxial materials can't fully absorb incident light,and the superlattice multi-layer heterointerface heterostructure is easy to grow a three-dimensional island-like structure,which makes the preparation of large-thickness materials more difficult.Therefore,how to obtain super-lattice detection materials with large thickness and high quantum efficiency becomes the key to further improve the performance of super-lattice detectors.In this paper,from the aspects of single-cycle growth structure and growth technology of superlattice,the epitaxial characteristics of superlattice heterostructure are made a profound study.By adjusting the V/?I beam ratio and In Sb interface layer conditions,the influence of conditions on T2SLs crystal quality and device performance with different growth were discussed.The specific research content are as follows:1.The effect of As/In beam ratio change on the crystal structure and surface morphology of In As/Ga Sb type ? superlattice materials during epitaxial growth of In As layer was researched.Due to the relatively large saturated vapor pressure of As,the background pressure of As will remain in the MBE cavity after the growth of the In As layer,which will affect the subsequent interface and the growth of the Ga Sb layer.Therefore,the optimization study of the epitaxial V/?I beam ratio of the In As layer is It is important to deeply understand the growth characteristics of superlattice materials.It was found that when the V/?I beam ratio was 1.90,the stable growth of the In As layer could not be maintained.A large number of macro defects began to appear on the surface of the prepared material,forming an island-like point structure where In atoms aggregated.When the V/?I beam current ratio gradually increased from 1.90 to 2.62,the point defects disappeared,and the AFM roughness of the microscopic surface morphology gradually decreased,but it still showed a three-dimensional island-like growth structure.As the V/?I beam current ratio increases,the lattice mismatch between the epitaxial layer and the substrate gradually decreases.The HRXRD curves analysis reveals that there is atomic exchange at the interface layer of the superlattice material.2.Design a new sequences of superlattice MBE growth structure,regulate the interface growth process,and explore the influence of the new growth structure and process on the crystal structure,surface morphology and luminescence characteristics of superlattice materials.In the In As/Ga Sb type ? superlattice MBE growth process,stress compensation can be effectively achieved by intentionally inserting an In Sb interface layer between the In As and Ga Sb layers.However,since In Sb and In As and Ga Sb have 0.65%and 0.59%lattices mismatch,respectively.Increasing the difficulty of growing high-quality interface layers.In this paper,the traditional interface growth method is redesigned,the direct growth of the In As-on-Ga Sb interface layer is eliminated,and it is introduced at the Ga Sb-on-In As interface.Sb beam infiltration deals with the problem of stress compensation.Through research,it is found that the microscopic surface of the superlattice material changes from a three-dimensional island growth mode to a two-dimensional layer growth mode under the new growth structure and process,but the Sb wetting time is important for the surface morphology,crystal structure and photoluminescence characteristics of the material as a result,inadequate Sb impregnation will make the interface area of the material more disordered,and the crystal structure integrity will be reduced,resulting in an increase in the surface roughness of the material,which will reduce the crystal quality of the superlattice and affect the photoluminescence characteristics.3.Verifying the advantages of the new growth process for the growth of large-thickness In As/Ga Sb type ? superlattice materials.As the number of periods increases from 500 to 800,the lattice mismatch between the epitaxial layer and the Ga Sb substrate of all samples can be controlled below 1×10-4,the FWHM of the first-order diffraction peaks are maintained at the level of 25 arcsec,and the surface root-mean-square roughness have not change significantly around 0.2 nm.The above data fully proves the new growth process has good stability and high repeatability in the preparation of large-thickness In As/Ga Sb type ? superlattice,which lays a certain foundation for the preparation of high-quality large-thickness In As/Ga Sb type ? superlattice.Provide a strong guarantee for the subsequent preparation of unit devices with large thickness and high quantum efficiency.4.Researching the uniformity and electrical characteristics of In As/Ga Sb type-? superlattice devices.8 points are selected at equal intervals on the surface of the 3-inch PIN device to testing.The lattice mismatch of each point is less than 5×10-5.The half-width of the first-order diffraction peak is about 25 arcsec.It is consistent with the designed growth thickness,which proves that this In As/Ga Sb type-? superlattice detector material has very high crystal quality and excellent uniformity.In terms of electrical properties,this device has a quantum efficiency of more than 80%at 4.6?m,under 77K temperature and 0 bias,and under-20m V bias,the dark current density is9.4×10-7A/cm2.The dynamic resistance area is 1.2×10-4?·cm2 under zero bias and the corresponding peak detection rate is 4.4×1012cm Hz1/2/W.Through the variable temperature I-V test and fitting,the dark current characteristics of the device are deeply analyzed.When it is below 80K,the dark current is mainly come from surface leakage current;when the temperature is 80?130K,the relationship between dark current density and temperature satisfies the formula:J?exp?Eg/2k B T?,at this time,dark current mainly come from generation–recombination current.When the temperature is higher than 130K,the relationship between the dark current density and the temperature satisfies the formula:J?exp?Eg/k B T?,at this time the diffusion current is dominant. |
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