结构缺陷对HgI_2晶体光吸收的影响

Effect of Structure Defect on Light Absorption of HgI_2 Crystal

为研究HgI2晶体结构缺陷与光吸收的关系,测试了晶体的UV和中红外透过光谱。结果表明,波长约为580nm时,存在着本征吸收限;波长大于580nm时,随波长增加,晶体对光的吸收减小,透过率达到45%以上;在1000～2500nm范围内,UV光谱存在四个明显的光吸收带,对应的入射光能量分别为0.79±0.01eV,0.72eV,0.57±0.01eV和0.53eV。中红外透过曲线随波长增加而增大,透过率为39%～68%。通过M/HgI2的I～t曲线,采用简单能级模型进一步确认了生长的HgI2晶体存在0.79±0.01eV和0.72eV两个陷阱能级。分析认为,HgI2晶体层间的相对移动形成的结构缺陷造成1572.5nm(0.79±0.01eV)和1729.2nm(0.72eV)处的吸收,晶体缺碘造成2117.5nm(0.57±0.01eV)处的吸收和汞空位造成2305.8nm(0.53eV)的吸收。在中红外波段,晶体结构缺陷造成了显著的晶格吸收。严格控制原料的化学计量比有利于减少HgI2晶体的结构缺陷,提高晶体的光学性能。

Optical properties of HgI2 crystal were investigated by UV-NIR-IR and M-IR spectra for understanding the relation between optical properties and structure defect of HgI2 single crystal. The results showed that the cut-off length of intrinsic absorption was about 580 nm in UV-NIR-IR spectra. The transmittance of the HgI2 single crystal increased with the increase of the wavelength,which the maxinum value was above 45%. Four absorption bands existed in the range of 1000-2500 nm,corresponding to 0. 79 ± 0. 01 eV,0. 72 eV,0. 57 ± 0. 01 eV and 0. 53 eV of energy of incident light,respectively. The transmittance of HgI2 crystal in the region 4000-500 cm-1 was 39% -68% with bullish trend. According to simple energy level model,the levels of 0. 79 ± 0. 01 eV and 0. 72 eV were further confirmed to be the absorption of trapping levels by I-t curves of M/HgI2. Through the discussions,it was suggested that the four absorption bands in UV spectra might be derived from the structure defects of as-grown HgI2 crystal,which formed with the considerable relative movement between the layers of HgI2 crystal（ 0. 79 ± 0. 01 eV and 0. 72 eV） ,the formation of mercury vacancy （ 0. 53 eV） and iodine deficiency （ 0. 57 ± 0. 01 eV） ,respectively. The structure defects of as-grown HgI2 crystal augmented the intensity of lattice absorption,which lead to the stronger lattice absorption in middle-infrared band. Optimization on stoichiometry of HgI2 crystal could reduce the structure defect and further increase optical quality.