Studies On Crystal Growth,Properties Of Cadmium Manganese Telluride And The Fabrication Of Magneto Optical Isolator

?-? compound semiconductor Cadmium Manganese Telluride(Cd_1-xMn_xTe or CdMnTe)has important applications in infrared lasers,magneto-optical switches,preparation of room temperature X-rays,g-rays detectors,etc,due to its excellent photoelectric properties;the unique magneto-optical characteristics play a very important role in the fields of magneto-optical isolators and magnetic field sensors.The CdMnTe crystal has a large forbidden band width,a continuously adjustable lattice parameter,and a structural coefficient of Mn which is close to 1 and so on.Due to the high melting point and high vapor pressure of Cd,the CdMnTe crystal grown by the traditional Bridgman method is prone to defects such as twins,Cd vacancies and composition segregation,which restricts the promotion and application of CdMnTe materials.Therefore,it is a problem to prepare a high quality CdMnTe crystal with uniform composition.In this paper,Cd_0.9Mn_0.1Te:V single crystal with Vanadium doping(concentration of5×10¹⁷ atoms/cm³)was grown by the Te?10%excess?solution vertical Bridgman method,this method can reduce the melting point of the system and reduce twin,get a single crystal with uniform composition.The effect of Te solution on solute transport during crystal growth was studied by improving the synthesis process and growth parameters of polycrystalline materials.The growth process of 30 mm diameter CdMnTe crystals was optimized by improved the feedstock,designed growth temperature and growth rate.The polycrystalline material synthesis temperature was 1363 K,the rocking time in the rocking furnace was 24 h,and the rotational speed was 1-3 r/min.The growth temperature of the single crystal was 1323 K,the growth rate was 0.1 mm/h,and the temperature gradient was 10-15 K/cm.After the growth of the single crystal,the upper and lower furnaces were kept at 1133 K for 96 h,to obtain a diameter of 30mm and a length of 100 mm Cd_0.9Mn_0.1Te:V ingot.X-ray diffraction,Electron Probe,Scanning Electron Microscopy,Transmission Electron Microscopy and Infrared Imaging were used to study the structure,defects and composition distribution of the crystal.X-ray powder diffraction results show that the preferential growth direction of Cd_0.9Mn_0.1Te:V crystal is[111]direction.The X-ray back-swing curve is highly symmetrical,the result indicate the composition and structure uniformity of the crystal is good.The planar micro-convex growth interface was analyzed by Infrared Imaging method.The main components of Cd_0.9Mn_0.1Te:V crystal were analyzed by Electron Probe.The uniformity and regularity of Mn distribution along the axial and radial directions of the ingot were studied.The results show that the segregation coefficient of Mn is close to 1.Scanning Electron Microscopy analysis show that the Te inclusion phase in the crystal is triangular,hexagonal and spherical.The surface of the crystal is distributed with parallel and"Y"type microcracks.The dislocation and Te precipitate phase in the crystal were observed by Transmission Electron Microscope.Infrared microscopy was used to study the distribution of Te inclusion phases in different axial positions of the ingot,with a size distribution ranging from 1-15?m and a density of2.104×10⁴⁷.62×10⁴ cm^-2.Fourier Transform Infrared Spectroscopy analysis show that the crystal transmittance of Cd_0.9Mn_0.1Te:V crystal is more than 55%,and the average transmittance in the middle of the ingot about 63.2%,which is close to the theoretical value of 65%.The cut-off wavelength of Cd_0.9Mn_0.1Te:V crystal obtained by Ultraviolet-Visible-near-Infrared spectroscopy is 775 nm,and the forbidden band width is 1.60 eV,which is close to the calculated value of 1.65 eV.Using I-V and I-T tests,the electrical properties and photoresponse of Cd_0.9Mn_0.1Te:V were studied.The bulk resistivity of the crystal is on the order of 10¹⁰?·cm.Under the action of 5 mW white light diode,the photocurrent was up to 32 nA,the ratio of photocurrent to dark current is up to11.The Hall effect results show that the conductivity type of CdMnTe crystal after Vanadium doping is n-type.The Faraday effect of Cd_0.9Mn_0.1Te:V crystal shows that the Verdet constant of Cd_0.9Mn_0.1Te:V crystal can reach up to 1369?°?/cm·T.The magneto-optical isolators were fabricated using the grown wafers,with isolation and insertion loss of 29 dB and 15 dB at 780nm operating wavelength,respectively.