Strong excitonic transition of Zn1−xMgxO alloy

Abstract

A strong excitonic optical transition in a ${\mathrm{Zn}}_{1-x}{\mathrm{Mg}}_x\mathrm{O}$ alloy grown by radical source molecular beam epitaxy was observed using both optical reflectivity measurements and photoluminescence (PL) measurements. Clear and strong reflectance peaks at room temperature (RT) were observed from $3.42\mathrm{eV}$ $(x=0.05)\text{to}4.62\mathrm{eV}$ $(x=0.61)$ from ZnMgO layers at RT. Distinct clear PL spectra at RT were also observed for energies up to $4.06\mathrm{eV}$ $(x=0.44)$ . The peak intensity of the reflected signal increased for $x$ values up to $x\sim 0.2$ simultaneously with an increase in PL intensity; however, a Stokes shift between the reflectance peak and the PL peak was not observed for $x$ values below 0.2. These facts suggest that the oscillator strength of ZnMgO is enhanced by alloying, and the underlying mechanism is discussed. Furthermore, we demonstrate that the strong reflectance properties even at RT provide an easy method to determine the Mg composition of a thin ZnMgO layer in a $\mathrm{Zn}\mathrm{Mg}\mathrm{O}∕\mathrm{Zn}\mathrm{O}$ heterostructure.