Structural and Optical Properties of Zn-Based II-VI Semiconductor Thin Films Deposited by MOCVD

Abstract

Polycrystalline ZnS/ZnO strained-layer superlattice and boron-doped ZnSe (ZnSe:B) thin films were deposited on soda-lime glass substrates using metalorganic chemical vapor deposition method. Then, the films were characterized by X-ray diffraction, Raman spectroscopy, optical absorption measurements. X-ray diffraction patterns of the superlattice film show peaks from both cubic ZnS and hexagonal ZnO, implying that the ZnS/ZnO strained-layer superlattice film was properly formed on the glass substrate. Only slight changes of the lattice constants of the superlattice (a'(ZnS) = 5.402 +/- 0.004 angstrom and c'(ZnO) = 5.221 +/- 0.003 angstrom) were observed compared to the single films (a(ZnS) = 5.410 +/- 0.004 angstrom, a(ZnO) = 3.245 +/- 0.003 angstrom and c(ZnO) = 5.208 +/- 0.003 angstrom). The Raman spectra of the superlattice film mainly exhibited phonon modes that belong to ZnS: 352 cm(-1) (1LO), 561 cm(-1) (2TO) and 786 cm(-1) (2LO). The measured direct bandgap energy of the ZnS/ZnO superlattice film was 3.40 eV, which is an intermediate value between the bandgap energies of ZnS (3.71 eV) and ZnO (3.20 eV). The lattice constant in the ZnSe: B films with a cubic structure was a(ZnSe:B) = 5.658 +/- 0.004 angstrom, which was smaller than undoped ZnSe, a(ZnSe) = 5.674 +/- 0.004 angstrom. Also, the bandgap energy of the ZnSe film decreased by B-doping from 2.83 eV to 2.92 eV. However, the electrical conductivity measured by using the van der Pauw method showed that B-doping does not improve the conductivity of ZnSe film.