Structural and nonlinear optical properties of self-assembled SnO2 -doped silicon nanorings formed by pulsed laser ablation

SnO2 -doped Si nanorings with an outer diameter of 25 nm and an average width of 5 nm are grown by pulsed laser deposition. Atomic force microscopy reveals several interesting self-assembling forms of polycrystalline as well as an amorphous type of silicon nanorings. Depending on the width of the ring, the optical bandgap and photoluminescence can be tuned from the near infrared (1.38 eV) to the ultraviolet (3.02 eV), giving evidence for the strong quantum confinement effect along the width of ringlike quantum states. From Z-scan studies, the two-photon absorption coefficient is determined to be 2.2× 10-6 m/W.