Study On Preparation Technology And Properties Of Au Doped HgCdTe LPE Materials With Large Size And High Quality

Because of its high performance,the HgCdTe infrared detector always plays an important role in the field of infrared detection.The modern advanced HgCdTe infrared focal plane arrays(IRFPAs)technology with the characteristics of large scale?high performance and low cost has made the demands on HgCdTe materials preparation technology.Large scale HgCdTe IRFPAs need the support of large size HgCdTe materials.High performance devices require improving the HgCdTe crystal quality and minority carrier lifetime inorder to suppress the dark current.The improvements of HgCd Te materials depend on the further research on the crystal defects.Low cost devices require new technology with low manufacture cost?high yield ? high reliability and high operating temperature.The n+-on-p device architechture is a widely used technology with great maturity.The key issue involved in n+-on-p is to improve the minority carrier lifetime in p-type HgCdTe.The Au doping technology is a feasible way to improve minority carrier lifetime,but the instability of the doped Au atoms need to be well understood and controlled.Facing the above requirements and problems,this dissertation studied the preparation techhnology and properties of Au-doped p-type HgCdTe materials with large size and high quality.The main highlights and innovative results are presented as follows:1.The large scale HgCdTe liquid phase epitaxy(LPE)technology was studied,and the 50 mm × 50 mm high quality HgCdTe films were prepared.By improving the design of the sample holder and applying the substrate back-protection technology,the size of HgCdTe film increased from 40 mm × 30 mm to 50 mm × 50 mm.The size of single piece film is doubled,and the total size of the LPE films in single run is increased by 50%.The materals' dislocation EPD is less than 1×105 cm-2.FWHM can reach 27.36??.The X-ray topography of the film is also quite uniform.The STDDEVs for the Cd composition and the thickness in single piece material are 0.0004 and 0.4 ?m,respectively.The uniformity of Cd composition and thickness has reached the advanced world levels.This obtained technology estabilished the foundation for enlarging IRFPA detectors' scale and yield.2.The in situ Au doping technology for HgCdTe LPE materials was studied.The method to accurately determine Au atoms segragation coefficient was achieved by SIMS measurement and the analysis.The segregation coefficient of Au atoms in long-wavelength HgCdTe Te-rich LPE process was calculated as 0.0085.The accurate control of Au doping concentration in HgCdTe materials was achieved.3.The effect of different annealing technologies on Au atoms distribution was studied,the mechanism on the migragation and diffusion of Au atoms in HgCdTe was achieved,and the annealing technologies to adjust Au doping atoms distribution were developed.In equilibrium,Au atoms concentration is proportional to Hg vacancy concentration in Au doped HgCdTe materials.In non-equilibrium,the Au atoms concentration will vary with Hg vacancy concentration because the diffusion of Au atoms is faster than Hg vacancy.Their concentration will keep dynamic equilibrium.Base on the relationship between Au atoms and Hg vacancy,the rules of Au atoms migration were explained that included(1)Annealing migrates the Au atoms into substrate;(2)Au atoms migrate in the post-ananealing process after the junction formation,which is caused by the interstitial Hg atoms induced by B+ implanation.It was also found that different annealing technologies such as Hg-rich?Te-rich and composite(Hg-rich plus Te-rich)annealing can change the Au atoms concentration distribution as positive gradient ? uniform and negative gradient distribution,respectively.These technologies can supply more choices for the application of Au doped HgCdTe materials.4.Taking account of the Au atoms migration in HgCdTe,the negative Hall coefficient of Au-doped sample after Hg-rich annealing was explained.After Hg-rich annealed,the Au atoms near the surface of the sample disappeares with the annihilation of Hg Vacancies.This process converts the top layer material to n-type in which the residual donors are predominat.But the deep layer remains p-type property if the annealing time is insufficient.Because the mobility of the electron is much larger than the hole,the overall Hall coefficient shows up as negative.In the Te-rich or composite annealed materials,the holes induced by the Hg vacancy and the Au acceptor are predominate,the behavior of the Hall coefficient with the changing of the temperature or the magnetic field intensity is similar to that of the pure Hg-vacancy materials.The only difference between these two situations is the difference of the activation energy at low temperature.The equivalent acceptor level of the Au doped materials is 13.3meV.The acceptor level of the Hg vacancy doped materials is 19.9meV.5.The effect of lattice mismatch on HgCdTe LPE materials property was studied systematically,it was found that the stress caused by the lattice mismatch in epilayer results in the mismatch dislocation,which had influence on the surface fine pattern.When the mismatch is in the range of ?0.004% and ?0.04%,lattice mismatch results in cross-hatch pattern with three-fold symmetry.This kind of pattern shows up in X-ray topography and surface topography.The cross-hatch pattern in Xray topography even becomes obvious after the mismatch is larger than 0.08%.The further analysis indicated the cross-hatch pattern originates from the <110> mismatch dislocations which are parallel to the surface.6.With the further increasing of mismatch,the transform of the cross-hatch pattern to the mosaic pattern takes place in the X-ray topography.When the mismatch is out of the range of 0.02%~0.11%,accumulation of mismatch dislocations may result in a change of crystal orientation thus favoring the apparition of facetted growth leading to macroscopic defects and macro voids.The materials surface will be occupied by the rough structure with the line roughness larger than 0.2?m.This study proposed a method to suppress this macro defect by controlling the lattice mismatch in a proper range.7.The prototype n+-on-p device based on Au-doped material was fabricated.The measured results showed the R0 A of the device with 14.3?m cut-off wavelength at 77 K reaches 0.1?cm2,which exceeds the level of the device based on Hg-vacancy materials.This result showed the superiority of Au doping technology.