Stress relaxation and transitions in optical bandgap of yttrium doped zinc oxide (YZO) thin films

• YZO thin films were grown on quartz by the least expensive sol–gel method.
• Vacuum annealing improved the crystallinity of YZO thin films.
• Grain size of YZO films were found to be increased by annealing.
• Stress relaxation were related to the tune of the bandgap in YZO thin films.
• PL provides the evidence of shifting the bandgap owing to stress release phenomena.

The stress relaxation and its effect on the bandgap of Y-doped ZnO (YZO) thin films were investigated by thermal annealing. YZO thin films were prepared on quartz glass by spin coating and subsequent annealed in vacuum. All the annealed YZO films showed a preferred (002) orientation. Photoluminescence (PL) provides the direct evidence of shifting the bandgap owing to stress release phenomena. The shifting in bandgap by increasing the annealing temperature can be attributed to the stress relaxation of YZO thin films. The bandgap of annealed films was initially decreased due to increase in magnitude of compressive stress and then increased as the tensile stress induced in the films. Therefore, these results may suggest the way to tune the band gap of YZO thin films by varying the residual stress through annealing.