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

点击翻译按钮获取中文摘要

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.