The spectrum of employment of ultra-thin layered materials in functional heterostructures and the precise control of their surface characteristics offer a remarkable platform to develop advanced optoelectronic devices. Herein, the wide bandgap and self-limiting surface oxides of Galinstan were innovatively employed as templates for the next sonochemical-assisted reactions to finally synthesize ultra-thin functionalized Ga2O3 nanosheets with tunable properties. To modulate the surface properties of the Ga2O3 nanosheets, various ionic solutions (aqueous AgNO3 and SeCl4) were used in the synthesis process. The decoration of the Ga2O3 nanosheets with Ag and Se nanostructures facilitated visible light responsivity of the Ga2O3 nanosheets. The functionalization of the gallium oxide nanosheets was also accompanied by unique rectifying behaviour of the Ga2O3 (Ag) based devices. The formation of either Schottky or Ohmic junctions between the Au electrode and Ga2O3 nanosheets and also the creation of type-II heterojunctions at the semiconductor heterointerfaces were the main controlling parameters of the optoelectronic devices. The implementation of the functionalized Ga2O3 nanosheets, as a complementary component of the optoelectronic device, enabled considerable improvement of the visible light responsivity in the TiO2-Ga2O3 films. Presenting both facile functionalization and controlling the properties of the nanosheets, this sonochemical technique can pave the way for further development of a new generation of ultrathin materials for optoelectronic applications.