Optical spectroscopy of ZnMgO thin films and heterostructures

Deep UV photon sensors based on wide bandgap semiconductors, such as II-oxides, III-nitrides, diamond, and SiC, can be used as biological and chemical sensors for environmental monitoring systems (e.g., ozone detection, water purification, determination of pollution levels in biological agents or in air). However, the bandgaps of diamond and SiC are not tunable, whereas those of AlGaN (composite III-nitrides) can only be varied from 3.4 eV to less than 4.5 eV through bandgap engineering, offering very limited multiple-bandwidth capabilities of detection.

The novel concept (proposed by the consortium of research groups from Taiwan, Latvia and Lithuania) is to use the originally developed ZnO-MgO pseudobinary system, which has tunable bandgap from 3.3 eV to 7.8 eV, thus significantly enhancing the ability of the sensor to detect signals at different energies simultaneously. Since optical properties and electronic structure of this novel ZnMgO material are not known, the fundamental physical properties will be explored: bandgap energy and its variation with temperature, optical transition mechanisms, thermal activation of carriers, structural homogeneity, influence of different substrates on defect formation, types of intrinsic defects (color centers), optical yield, etc.
The goal of doctoral work proposed is to thoroughly investigate optical properties of ZnMgO thin films and heterostructures, grown using molecular beam epitaxy (MBE):
  • wurtzite Zn(1-x)MgxO epilayers and Zn(x)Mg(1-x)O/MgO heterostructures with x= 0.7-0.5 on a low lattice-mismatch ScAlMgO4 (SCAM) substrate;
  • rocksalt Zn(1-x)MgxO epilayers and Zn(x)Mg(1-x)O/MgO heterostructures with x= 0.2-0.5 on a low lattice-mismatch MgO and Cu2O substrates.
The spectroscopic and calculation results obtained will be used as crucial feedback to elaborate optimal technological parameters.
For more information, please contact the theme supervisor R. Nedzinskas.