The origin of electrical property deterioration with increasing Mg concentration in ZnMgO:Ga

► The growth conditions of epitaxial ZnMgO:Ga via PLD are optimized. ► Resulted TCO films have the highest conductivity among works of the same Mg ratio. ► Increasing Mg leads to similar crystal quality but inferior σ, n, μ. ► Decrease in crystallinity further deteriorated σ, n, μ.