Studies on the Strain in Manganese (II)-Doped Metal-Chalconide Films and Their Luminescent Properties

用电子自旋共振(ESR)谱研究了含Mn(II)的超晶格的光致发光(PL)中观察到的反常现象，与用热壁外延方法生长在GaAs(100)衬底上的ZnS：Mn、CdS：Mn和CdTe：Mn薄膜相比，当磁场垂直于薄膜厚度时，当磁场垂直于薄膜厚度时，最低能量跃迁分裂为三重态或五重态。对这两个光谱的计算机模拟证实，所得到的ESR参数与立方结构单晶的ESR参数相对应，尽管它们的表观线形是不同的。推测这种差异是由于薄膜和衬底之间的晶格失配引起的Mn(II)周围晶场的单轴形变所致。在GaAs(100)衬底上生长的CdTe：Mn薄膜也观察到类似的现象。对于CBS：Mn-ZnS超晶格，观察到g值负移，这表明硫化镉薄膜中Mn(II)与其周围环境的共价性受硫化锌和硫化镉交替层之间晶格失配的影响。在室温下，还发现了六条超精细谱线，其超精细分裂常数比大块晶体窄。这不仅是由于Mn-Te键长的压缩变形，也是由于Te向Mn(II)的电子转移不明显而导致键本身的离子性增加所致。这导致了CdTe的价带和/或导带相对于Mn(II)的3d^5能级的变化。由此得出结论：在室温下观察到的异常红光是由于在CdTe：Mn层中发生的这些剧烈变化所致。

Electron spin resonance (ESR) spectroscopy has been applied to investigate unusual phenomena observed in the photoluminescence (PL) of Mn (II)-containing superlattices of CdS : Mn-ZnS and CdTe : Mn compared with thin films of ZnS : Mn, CdS : Mn and CdTe : Mn, which were grown on a GaAs (100) substrate by means of hot wall epitaxy.For the ZnS : Mn thin films the lowest-energy transition assigned to M_I=-5/2 splits into either a triplet or quintet depending on the thickness of the film when the magnetic field normal to it. Computer simulation of both spectra confirmed that the ESR parameters obtained correspond to those for a single crystal of cubic structure, although the apparent lineshape are different each other. It is presumed that the difference is due to the uniaxial deformation of the crystal field surrounding Mn (II) derived from the lattice mismatch between the films and substrate. Similar phenomena are observed for the CdTe : Mn films on GaAs (100) substrate as well. However, there is no difference appeared in PL between those thin films and the bulk crystals.For the CbS : Mn-ZnS superlattices a negative shift of g-value is observed, implying that the covalency between Mn (II) and its environment in CdS layr is affected by the lattice mismatch between the alternate layrs of ZnS and CdS.For the CdTe : Mn-ZnS superlattices narrow six hyperfine lines with a large hyperfine splitting constant compare with that of the bulk CdTe : Mn crystals are also found at room temperature. These result not only from the compressive distortion of the Mn-Te bond length but also by an increase in the ionicity of the bond itself due to electron transfer from Te to Mn (II) being less significant. which leads to the change in the valence and/or conduction bands of CdTe relative to the 3d^5 energy levels of Mn (II). Consequently, it is concluded that the unusual red luminescence observed at room temperature is due to these dramatic change happened in the CdTe : Mn layrs.