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

用电子自旋共振（ESR）谱研究了在GaAs（100）衬底上用热壁外延生长的ZnS：Mn、CdS：Mn和CdTe：Mn薄膜的光致发光（PL）中所观察到的异常现象。Mn薄膜的最低能量跃迁M_I=-5/2，在垂直于薄膜的磁场作用下，随薄膜厚度的不同，分裂为三重态或五重态.计算机模拟两种谱的结果证实，所获得的ESR参数与立方结构单晶的ESR参数一致，虽然外观线形彼此不同。据推测，这种差异是由于薄膜和衬底之间的晶格失配所产生的Mn（II）周围的晶体场的单轴变形。对于GaAs（100）衬底上的CdTe：Mn薄膜也观察到了类似的现象。对于CbS：Mn-ZnS超晶格，观察到g值负移，表明Mn（II）与CdS层间的共价性受到ZnS和CdS交替层间晶格失配的影响;对于CdTe：Mn-ZnS超晶格，观察到g值负移，表明Mn（II）与CdS层间的共价性受到ZnS和CdS交替层间晶格失配的影响。Mn-ZnS超晶格在室温下具有较窄的六条超精细线，且超精细分裂常数比CdTe：Mn体晶体大。这些结果不仅从Mn-Te键长的压缩变形，但也通过增加键本身的离子性，由于从Te到Mn（II）的电子转移是不太显着。这导致CdTe的价带和/或导带相对于Mn（II）的3d^5能级的变化。因此，可以得出结论，在室温下观察到的不寻常的红色发光是由于这些戏剧性的变化发生在CdTe：Mn层。

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.