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.