Laser annealing of Au/HfO < inf > 2 < /inf > bi-layers to fabricate Au nanoparticles without altering the phase of HfO < inf > 2 < /inf > for applications in SERS and memory devices

Abstract

We report an athermal laser annealing technique to fabricate a high-density array of gold nanoparticles on the surface of hafnium oxide thin films without altering the phase of HfO2. Au (~ 5 nm) films deposited on amorphous HfO2 (~ 10 nm) are subjected to laser annealing by using an Excimer laser (248 nm) to produce Au nanoparticles. It is important to note that the usual thermal methods would change the phase of the HfO2. It is observed that the size of the spherical Au nanoparticles decreases and their surface density increases as the number of laser pulses increases. These Au nanoparticles has induced a significant enhancement in the Raman signature of the standard R6G dye. Further, Metal–Oxide–Semiconductor capacitors were fabricated by depositing another layer of HfO2 followed by metal contacts on the surface of these nanoparticles. The leakage current conduction through the gate oxide with and without embedded nanoparticles has been studied using the Poole–Frenkel and Fowler–Nordheim tunneling mechanisms by examining the leakage current–voltage characteristics. PF tunneling is found to be prominent in these MOS structures with Au nanoparticles, which is attributed to the possible charge trapping by the embedded Au nanoparticles. The capacitance–voltage (C–V) characteristics show a significant broadening in the hysteresis loop indicating the improvement in the storage capacity of these MOS capacitors.