Investigation of nonlinear optical properties in GaN nanoparticles and nanosheets spanning deep ultraviolet to near-infrared wavelengths

Abstract

The nonlinear optical behavior of the wide bandgap semiconductor gallium nitride (GaN), manifested in both its crystalline and film forms, has garnered significant attention. Considering the modified properties when GaN is reduced to nanometer scale, a comprehensive investigation of the nonlinear optical properties of GaN nanomaterials across the spectral range from deep ultraviolet to near-infrared was conducted using ultrafast picosecond pulse lasers. When subjected to lower peak power lasers, these nanomaterials displayed a broadband saturable absorption effect resulting from single-photon absorption. In contrast, exposure to higher peak power lasers led to a reverse saturable absorption effect, driven by two-photon or three-photon absorption, covering wavelengths from deep ultraviolet to infrared. Utilizing the semiconductor band structure model, the electron transition mechanisms from the valence band or defect states to the conduction band were analyzed. At the wavelengths of 266 nm, 355 nm, 532 nm, and 1064 nm, the modulation depths of the saturable absorption effect observed in GaN nanosheets were calculated as 57.03%, 109.15%, 376.23%, and 76.03%, respectively. Concurrently, the minimum normalized transmittances associated with the optical limiting effect at these wavelengths were recorded at 17.46%, 25.27%, 30.06%, and 41.68%. Comparative analysis reveals that nonlinear effects are more pronounced in GaN nanomaterials than in bulk materials, attributed to their nanoscale dimensions and an increase in defect density. Experimental finding demonstrates that GaN nanosheets and nanoparticles hold substantial promise as broadband nonlinear optoelectronic devices, particularly serving as rare saturable absorbers and optical limiters for ultraviolet and deep ultraviolet laser. This study provides a direction for research on wide bandgap semiconductor nanomaterials as nonlinear absorption materials and underscores their significant application value.