Enhancement of photoluminescence in RF sputtered ZnMgO thin films by optimizing annealing temperature

Zn _0.85Mg _0.15O a promising material for the future in the area of the optoelectronic devices due to the flexibility of changing bandgap. The impact of thermal annealing on Zn _0.85Mg _0.15O thin films grown by RF sputtering on intrinsic Si substrate by RF sputtering at constant temperature 400°C. During deposition gas flow 80% Argon and 20% oxygen was used. The samples were rapid thermal annealed at 900°C (20 sec) and 950°C for 20 and 30 sec to yield samples A, B and C, respectively. Low temperature photoluminescence (PL) measurements show presence of violet emission around 3.1 eV in as-grown sample due to the presence of zinc interstitial defects. Near-band-edge emission was found at around 3.65 eV for sample A. However, for sample B this peak was redshifted and found around 3.63 eV but with much higher intensity. Further increase on annealing time (30 sec) sample was further red-shifted (sample C). On comparing with sample a, sample B showed 3 times enhancement in PL intensity and 30 times enhancement compared to as grown sample. X-ray diffraction measurements confirmed the growth of highly c-axis oriented <002> Zn _0.85Mg _0.15O thin films for all samples. Uniform lattice constant (a= 0.29 and c= 0.51 nm) was achieved for all annealed samples. The <002> peak for all annealed samples shows higher intensity in comparison with the as-grown. A slight shift in the peak was observed which is due to presence of strain. For sample B surface roughness were measured 6.34nm.