M. Ahn, A. Sarracino, A. Ansari, B. Torralva, S. Yalisove, and J. Phillips
Unique material modifications of Ga2O3 enabled by ultrafast laser irradiation

Ultrafast (femtosecond pulse) laser irradiation provides unique laser-material interactions associated with high instantaneous electric fields and short timescales that lead to a nonequilibrium state between excited electrons and phonons. These interactions result in material modifications that differ from conventional chemical, physical, and thermal processing at much longer timescales, and an opportunity to address material and device processing challenges associated with wide-bandgap materials such as Ga2O3. In this work, we explore ultrafast laser irradiation (Ti:sapphire, 150 fs pulse width) of bulk (010) Sn-doped β-Ga2O3 under two different wavelengths, fundamental (780 nm) and frequency-doubled (390 nm), and a range of laser fluences. We identified a regime for laser-induced damage threshold resulting in material ablation, thermally-induced straight crack formation, and recrystallization. Rastering on a β-Ga2O3 substrate created surface nanostructures including laser-induced periodic surface structures at a high spatial frequency (period ~250 nm). These highly aligned periodic structures can be controlled by laser polarization and wavelength, presenting a means for direct writing of surface nanostructures. Enhanced atomic movement associated with a transient metallic state can provide a means for intentional generation of point defects via the laser irradiation. These point defects may offer a means of electrical modification, which was demonstrated as more than five orders of the magnitude enhancement of lateral conductance on rastered β-Ga2O3. Moreover, a hydrophobic surface of β-Ga2O3was achieved by ultrafast laser irradiation.

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