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.
In this paper, during InAs/GaAs (001) quantum dot molecular beam epitaxy growth, four-beam pulsed laser-interference was used to in-situ irradiate on the wetting layer with an InAs coverage of 1.1 monolayer. Significant atomic layer removal and periodic nanostructures including nanoholes and nanoislands were obtained. These periodic nanostructures had a significant influence on quantum dot growth. Especially for the structure of nano-island, quantum dots preferentially nucleated at the edges of them. When the nano-island size becomes small enough, ordered quantum dot arrays are directly achieved on smooth GaAs surface with a follow-up InAs deposition accompanied by the disappearance of the nanoislands. This finding provides a potential technique leading to site-controlled and defect-free quantum dot fabrication.