Strain-Controlled Silicon Patterning on Sapphire Wafer by Ultrafast Laser-Induced Backward Transfer

Strain engineering of patterned silicon on a sapphire wafer is achieved by modulating the spatial confined plasma during ultrafast laser-induced backward transfer. High-energy laser-ablated silicon plasma can be generated within the confined space, where a transitional SiO layer is formed in the silicon-sapphire interface. Heat transfer to sapphire can thus be hindered, which is beneficial for thermal accumulation in silicon and crystallinity improvement. Meanwhile, tensile strain can be induced in the deposited silicon to coordinate the lattice mismatch at the heterojunction and the difference in thermal expansion coefficients between silicon and SiO. By increasing the incident laser power, the tensile strain can increase from 0.265% to 0.354%. This tensile-strained silicon is stable with negligible relaxation after thermal annealing at 600 °C. The strained silicon on the sapphire (SOS) structure fabricated at a laser power of 2.5 W shows a peak carrier mobility of 465 cm² V^-1 s^-1, with an enhancement factor of 3.2 compared with that of the unstrained SOS. Furthermore, the strained silicon shows a mobility retention of more than 85% even after thermal annealing at 600 °C for 3 h. This strained SOS structure therefore shows great potential in the development of high-performance electronic and optoelectronic devices.