Incorporation and optical properties of magnesium in cubic GaN epilayers grown by molecular beam epitaxy

The incorporation and optical properties of Mg in cubic GaN $\mathrm{(c-}\mathrm{GaN})$ epilayers grown by rf plasma-assisted molecular beam epitaxy on (100) GaAs are investigated by secondary ion mass spectroscopy and low-temperature photoluminescence (PL). By varying the Mg flux by more than four orders of magnitude, the incorporation of Mg saturates at high Mg flux and is limited to a value of about ${\text{5×10}}^{18}\hspace{0.17em}{\mathrm{cm}}^{\mathrm{-3}}$ due to the high volatility of Mg at growth temperature. In addition, we observe an accumulation of Mg at the GaN/GaAs interface due to a diffusion of Mg to the GaAs substrate. Low-temperature PL spectra reveal several well-separated lines. Besides a shallow acceptor level at $E_A\text{≅0.230\hspace{0.17em}}\mathrm{eV},$ additional Mg-related deep defect levels indicate an incorporation of Mg at off-gallium sites or as complexes.