The atomic layer deposition (ALD) technique has attracted significant attention because it enables the control of film synthesis at the subnanometre scale. Herein, molybdenum oxide (MoO₃) ultrathin films using the ALD system through Bis(t-butylimido)bis(dimethylamino)molybdenum (VI) as a molybdenum (Mo) source are prepared. To understand the effect of deposition temperature, thin films are prepared at three different temperatures 100, 150, and 250 °C. The morphological and elemental properties are assessed using a field emission scanning electron microscope, scanning transmission electron microscopy, and energy-dispersive X-ray spectroscopy techniques. It is observed that the film thicknesses increase with the increase in the deposition temperature. It is found that the film growth at 150 °C is the most potential one for UV optoelectronic applications with high stability even under low applied bias voltages. Moreover, these films show interesting nonlinear optical behaviors as investigated with the z-scan technique applying open and closed aperture methods. The calculated nonlinear optical parameters including nonlinear absorption coefficient (β), nonlinear refractive index (n ₂), nonlinear refractive coefficient (γ), and third-order nonlinear susceptibility (χ ⁽³⁾) are 10⁻¹¹ m W⁻¹, 10⁻¹⁶ cm² W⁻¹, 10⁻¹¹ cm² W⁻¹, and 10⁻¹¹ esu, respectively.