  Mg0.29Zn0.71O/ZnO (MZO/ZnO) bilayers were grown on sapphire substrates by
pulsed laser deposition at ~ 400 C and were subsequently annealed at different
temperatures ranging from ~ 500 to 900 C to allow diffusion of Mg across the
interface. The diffusion of Mg was confirmed from secondary ion mass
spectroscopy (SIMS) and Photo-absorption measurements on the samples. As a
result of Mg diffusion the photoluminescence (PL) spectra of the bilayers got
significantly modified. Whereas the as grown structure had two distinct near
band edge UV luminescence peaks corresponding to the ZnO and MZO layer, the one
annealed at ~ 900 C had a single near band edge PL peak corresponding to a
complete intermixed layer. At the intermediate annealing temperature of ~800 C
the PL peak position corresponding to the MZO layer red-shifted while that
corresponding to the ZnO layer blue-shifted, implying a diffused interface and
partial intermixing. A theoretical model has been developed and numerically
simulated to correlate the PL spectra of the bilayers with the Mg diffusion
profile across the interface, as measured by SIMS.
