Band offsets, electron affinities and optical dynamics at the CdBr2/SiO2 interfaces

Abstract

Herein, the structural, optical, dielectric and optical conductivity parameters of the CdBr2/SiO2 interfaces are reported. Thin films of CdBr2 are coated with 50 nm thick SiO2 under a vacuum pressure of 10−5 mbar. The structural morphological and optical investigations have shown that CdBr2 exhibit hexagonal structure of lattice parameters of a=b=7.20Å and =13.86Å, energy band gap of 3.32 eV and Urbach energy of 0.84 eV. The interfacing of CdBr2 films with SiO2, shortened the lattice parameters, blue-shifted the energy band gap and decreased the Urbach energy value. The electron affinity of CdBr2 which is determined here is found to be 3.27 eV. The CdBr2/SiO2 interfaces displayed a conduction and a valence band offsets of 2.37 eV and 3.21 eV, respectively. In addition, the dielectric dispersion and optical conduction analyses using the Drude-Lorentz approach have shown that the drift mobility and plasmon frequency (Wpi) of the free charge carriers at the CdBr2/SiO2 interfaces varies in the range of 28.59–22.87 cm2/Vs and 0.41–6.47 GHz, respectively. The effectiveness of the plasmon frequency to limit signal propagation in the heterojunction devices is confirmed by the impedance spectroscopy technique which showed radiowave (RF) band filter characteristics at the targeted Wpi. The energy band offsets, the optical conductivity parameters and the RF filtering properties nominates the CdBr2/SiO2 heterojunctions for use in thin film transistor technology.