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

应用电子自旋共振（ESR）光谱研究了含Mn （II）的CdS: Mn-ZnS和CdTe: Mn超晶格的光致发光（PL）现象，并与在GaAs（100）衬底上通过热壁外延生长的ZnS: Mn、CdS: Mn和CdTe: Mn薄膜进行了比较。对于ZnS: Mn薄膜，根据薄膜的厚度，分配给m_1 =-5/2的最低能量跃迁分为三重态或五重态。对两种光谱的计算机模拟证实，所得的ESR参数与立方结构单晶的ESR参数一致，尽管表观线形各不相同。可以推测，这种差异是由于薄膜和衬底之间的晶格不匹配引起的Mn （II）周围晶体场的单轴变形。在GaAs（100）衬底上的CdTe: Mn薄膜也观察到类似的现象。然而，这些薄膜与体晶体之间的PL没有差异。对于CbS: Mn-ZnS超晶格，观察到g值的负移，这意味着CdS层中Mn （II）及其环境之间的共价受到ZnS和CdS交替层之间晶格失配的影响。对于CdTe: Mn- zns超晶格，在室温下也发现了与CdTe: Mn晶体相比，具有较大超细分裂常数的六条窄超细线。这些结果不仅是由于Mn-Te键长度的压缩扭曲，而且由于从Te到Mn （II）的电子转移不那么显著，键本身的离子性增加。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CdTe: Mn层发生了这些剧烈的变化。

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.