MBE growth and optical properties of ZnO on GaAs(111) substrates

Hexagonal ZnO layers were grown by plasma assisted MBE on GaAs(111)B substrates. The substrate was chemically etched and no buffer layer was introduced. The epitaxial orientation relationships was ZnO(0001)//GaAs(111) and ZnO[11–20]//GaAs[01–1]. The layer–substrate interface was investigated by transmission electron microscope (TEM) observation, and 2–3 monolayer thick contrast band was found at the interface. The lattice constant c was smaller than that of bulk ZnO and changed systematically with the layer thickness. Low temperature photoluminescence (PL) spectra was dominated by a donor bund exciton band at 3.360 eV. Another bound exciton band was found around 3.330 eV. The relative intensity of the PL bands changed with growth conditions. PL peak energies became smaller as the lattice constant c became smaller. The lattice strain dependence of the exciton energy was derived.