Synthesis,Crystal Growth And Defects Of IR-NLO Crystal CdSiP₂

Infrared coherent optic sources have wide applications in the molecular resonances,medical surgery,and infrared countermeasure.Nonlinear frequency conversion is one of the most powerful technique for the generation of mid-infrared laser,in which the infrared nonlinear optical(IR-NLO)crystals are crucial materials for the devices fabrication.In the last several decades,the chalcopyrite semiconductors including AgGaSe2,AgGaS2,ZnGeP2(ZGP),CdGeAs2,and CdSiP2(CSP)have attracted great attention as the main class IR-NLO materials due to their unique physical properties.Among them,CdSiP2 possesses the excellent optical merits.The transparent range of CdSiP2 is in the range of 0.5-10 ?m,and the laser damage threshold(>30 MW/cm2@1.064 ?m)is higher than that of sulfide crystals.The appropriate negative birefringence(-0.05)of CdSiP2 offers the phase matching for 1,1.5,and 2 ?m lasers pumping,and the non-critical phase matching is achievable by the most common Nd3+laser with idler output in the 6 ?m range.In addition,the nonlinear optical coefficient of CdSiP2(d36=84.5 pm/V)is the highest one among the crystals which can be pumped by 1064 and 1550 nm lasers without two photon absorption phenomenon.These unique optical properties,along with a relatively high hardness(9.3 GPa)and thermal conductivity(13.6 Wm-1K-1)make CdSiP2 attractive for frequency down-conversion applications for the generation of laser in 1-9 ?m range.The main contents of the thesis are as follows:The performance characteristics and development trend of single crystal of phosphorus ternary compounds are reviewed,and the crystal growth technology of bridgman method is introduced in detail.In this paper,the research progress of CdSiP2 crystal ultrafafer laser output is systematically reviewed.Based on these reviews,the basis,purpose and main research contents of this paper are presented.Two-temperature CdSiP2 polycrystalline synthesis furnace was independently designed,and the temperature field in this furnace was modified to ensure that CdSiP2 polycrystalline material is synthesized safely and efficiently.CdSiP2 polycrystalline was synthesized by one-temperature zone method and two-temperature zone gas phase transport method separately.We have improved the synthetic amount by optimizing the processing technology.CdSiP2 polycrystalline materials with high purity density and good crystallization quality can be synthesized at least 140g in one synthesis run by using the two-temperature zone method.The synthesis period was shortened from 14 days to less than 7 days,which improved the efficiency of CdSiP2,polycrystalline synthesis.What's more,we systematically studied the transport phenomena and the intermediates in the hot zone at different stages and temperatures during the synthesis of CdSiP2.The results show that the two-temperature zone synthesis of CdSiP2 includes two steps:the formation of binary phosphorous cadmium compounds,and the reaction with silicon to form CdSiP2.When the temperature of high-temperature area is below 850?,the main reaction intermediates for CdSiP2 synthesis are CdP2 and Cd2P3.When the temperature is higher than 1050?,CdSiP2 begins to form.Stable growth of CdSiP2 crystal with diameter ?12 mm by spontaneous nucleation.The problems of crystal cracking and pores on the surface of the crystal were solved,which provided a strong guidance for the later directional seed growth of CdSiP2 crystal.CdSiP2 crystal with dimensions of 15 mm in diameter and 60 mm in length has been successfully grown by using the seed.The difficulties of seed fusion,crystal orientation and crystal processing were solved,further improving the utilization rate of the crystal.HRXRD was used to characterize the crystal quality of CdSiP2.The structural quality of CdSiP2 single crystals was estimated from the rocking curves.The shape of the peak had a good symmetry,and the full width at the half maximum(FWHM)of the peak for the as-grown CdSiP2 single crystal of the(004)was 40".The effect of crucible descending speed and crucible rotating speed on crystal growth of CdSiP2 was investigated.The crucible descending rate was generally 0.2-0.5 mm/h.In addition,the crucible needs to be added to rotate,and the speed was generally 5-10 r/min.The transmittance spectrum of CdSiP2 crystals were characterized.The transmittance range of CdSiP2 crystals was in the range of 0.5-10 ?m.The reason and suppression measures of CdSiP2 crystal cracking were studied.EPR technique was used to characterize the impurity defects in the as-grown CdSiP2 single crystal.The typical hyperfine structure of Mn2+ was measured at room temperature.The substitution defect of Fe+(3d7)replacing Cd2+in the crystal was measured at 2 K temperature,and the GDMS was used to analyze the impurity content of the csystal.The results show that the transition metal elements Fe,Mn,Ti,Cr and the main group metals Al,Mg and Na are high in the crystal.These metal impurities can displace the position of Cd or Si in the crystal,forming a displacement point defect.By contrast,it was determined that the strong absorption of the crystal at 1.78 ?m was caused by Fe+impurities.The annealing effects on infrared transmittance of CdSiP2 single crystal were studied in detail.The results show that the ultraviolet cutoff edge of the three samples did not change,and the transmittance in the visible near-infrared band increased after annealing in P,CdP2 and CdSiP2 atmosphere at 750? for 150 h.While after annealing in CdSiP2 intrinsic atmosphere,the small absorption peak of the wafer near 700 nm disappears and no new absorption peak appears.The absorption coefficient of CdSiP2 can be decreased to 0.18 cm-1 at 1064 nm,improving the crystal quality.These results provide guidance for the application of CdSiP2 crystal devices.