In-doped CdTeSe Crystals Growth And Their Defects Control

CdTeSe crystals have high resistivity and low defect density,and has high composition uniformity,which can effectively avoid the composition segregation caused by the high segregation coefficient(～1.35)of Zn in CdZnTe crystal.Therefore,it is promising that CdTeSe crystals are will become a new generation of crystal materials for radiation detectors.In this paper,In-doped CdTeSe crystals were grown in excess Te environment by vertical Bridgman method.The synthesis and growth process of the crystal were studied.The influence of defect distribution in the crystal on the photoelectric properties of the material was analyzed.CdTeSe crystals were grown by vertical Bridgman method and the theoretical In-doping amount is 10-15 ppm.Through the synthesis of polycrystalline and single crystals growth,two CdTeSe ingots with a diameter of 15 mm were successfully grown without cracks on the surface and no obvious twins/grain boundaries.According to the phase analysis,the CdTeSe crystals have a single crystal diffraction peak on the(111)crystal plane,the composition is a single zinc blende structure,and the crystal quality is good.Through the AFS analysis,the segregation coefficient of Se in the CdTeSe crystal is calculated by fitting to be 1.006 and the Se element is uniformly distributed in the CdTeSe ingots and there is no component segregation.The optical characterization results show that the band gap of CdTeSe crystals is about 1.4 eV,and the infrared transmittance is 60%,which is close to the theoretical value.The main size of Te inclusion phase is 5-10 μm,and the average density is on the order of 104 cm-2.The scattering effect of the Te-rich relative to infrared light in the crystal will cause the transmittance of some wafers to decrease.The existence of the Te-rich phase affects the distribution of impurities in the crystal and causes defects.The electrical performance characterization results reveal the electrical properties of the CdTeSe crystal.The deep-level defects pin the Fermi level in the forbidden band to achieve high resistivity.The resistivity of CdTeSe crystal can reach the order of 1010Ω·cm,the light response is fast,and it has a higher switching ratio in the visible light band.In the thermal equilibrium state,Cd vacancies are not completely compensated by In donor doping,and the majority of carriers in the crystal are holes.Defect analysis was carried out through Raman and PL spectroscopy and it can be observed that there are Te-related A1 modes and Te "triangular" lattices(E1,A1,TO/E2)in the CdTeSe crystal,and secondary phonon modes with A1 and E symmetry,and the CdTe-like longitudinal optical phonon mode LO.The integrated intensity of PL spectrum of CdTeSel-2 wafer increases with temperature between 30-50 K,showing an abnormal temperature dependence phenomenon.The existence of the Te-rich phase in the crystal will cause mismatch and disorder in the surrounding lattice,resulting in lattice defects and the formation of intermediate states,resulting in lattice relaxation and "negative thermal quenching".There are two main luminescence peaks in CdTeSe crystals:donor-bound exciton peak(D0,X)and defect composite luminescence peak Dcomplex.The Dcompiex peak is mainly caused by the luminescence peak D1 caused by the A center related to the Cd vacancy.The red shift of the luminescence peak is due to the high degree of self-compensation while being doped.The analysis believes that it is due to the introduction of the donor energy level InCd+ after In occupying the Cd site in the CdTeSe crystal,which recombines with the Cd vacancy,forming shallow acceptor defects[VCd2-·InCd+]-.and then generate a neutral defect complex[VCd2-·2InCd+]0.thereby reducing the doping efficiency and generating a self-compensation effect.The TeCd2+deep-level defect formed by the reaction of VCd2-with Tei produces the Fermi level pinning effect,which make the CdTeSe crystals obtain high resistivity.