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Observation of using laser direct writing to fabricate nano-grooves on GaAs substrate

In this paper, we presented a study of fabricating nano-grooves on GaAs substrate through laser direct writing (LDW). GaAs (001) substrate with homo-deposition of 500nm buffer layer was linearly scanned (pixel by pixel) by a focused UV laser (405nm) to directly create nano-grooved structures. The dependence of laser power and dwelling time (the exposure duration for each scanning pixel) on the patterned grooves were carefully observed. First, with the fixed setting of dwelling time at 10000ns, the laser power was varied from 110mW to 140mW. It can be found that there is an ablation threshold power between 115mW-120mW. As the power exceeds 125mW, as well as the depth, the average full width at half maximum (FWHM) of grooves could be effectively turned with a positive correlation to the power. Then, with the fixed setting of power at 130mW, a wide dwelling time variation from 10000ns to 10ns was systematically investigated. It is observed, in the range of 10ns-4000ns, the average depth can be continuously tuned by the dwelling time following an approximately linear positive relation, but once above 4000ns, the average depth will be saturated at ~77nm. While for the average FWHM, the saturation will show up early just when the dwelling time is above 100ns and the saturated value is ~90nm. Moreover, if the dwelling time is set too small (below 50ns), a by-product of nano-dots can form in the grooves.