Nanostructured surfaces

Optical properties of CdTe doped Li
Mazur T.M. 1, Slyotov M.M. 2, Kinzerska O.V. 3, Prokopiv V.V. 1

1 Department of Physics and Chemistry of Solid State, Faculty of Physics and Technology, Vasyl Stefanyk Precarpathian National University, Shevchenko Str., 57, Ivano-Frankivsk-76018, Ukraine.
E-mail: tetiana.mazur@nung.edu.ua
2,3 Department of Optics and Publishing and Printing, Department of Semiconductor Physics and Nanostructures, Applied-physics and computer sciences Institute, Yuriy Fedkovych Chernivtsi National University, Kotsubinskiy Str., 2, Chernivtsi-58012, Ukraine 
In this paper, the optical and luminescent properties of undoped CdTe and surface layers of CdTe specially doped with Li impurity were studied. Doping was carried out in a water suspension of LiNO3. The optical transmission and photoluminescence spectra were studied and the formation of a surface nanostructure was established. The optical processes of absorption, reflection, and luminescence were studied using a universal optical setup, which made it possible to carry out measurements both by the classical technique and using the λ-modulation method. For the excitation of luminescence on the obtained CdTe:Li layers, a LGN-21 nitrogen laser with exciting radiation with λ = 0.337 μm (ω ~ 3.68 eV) was used. The measured signal was recorded using a synchrodetection system. It was established that doping of CdTe with Li impurity from a water suspension does not affect the dependence of the optical absorption curves and the value of the basic material parameter1,5 еV. This indicates the absence of the influence of alloying processes on the properties of the volume of the base material. A study of the photoluminescence of CdTe: Li detected intense radiation. Its spectrum consists of two bands, which are determined by recombination processes in the edge region ℏω⁓Eg and a wide component in the photon energy range ℏω >> Eg with a quantum efficiency of 5-7%. Note that no luminescence is observed on the output crystals. This indicates the formation of a thin, alloyed with Li surface nanostructured layer, the radiation of which is due to quantization of the energy of the charge carriers due to the formation of the nanostructure. A study of-modulated optical reflection was carried out, which determined the parameters of the band structure of the base substrates and the resulting  layers CdTe: Li 1.5 eV and 0.9 eV and optical processes on a modified nanostructured surface. It was shown that doping of CdTe with Li impurity in a water solution does not change the properties of the base material but it contributes to intense luminescence. Defined technological modes of doping allow one to obtain an inversion of conductivity with n-type to p-type.