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.
We have investigated the modification of self-assembled InAs/GaAs quantum dots (QDs) by in situ pulsed laser irradiation. The QDs were fabricated by molecular beam epitaxy (MBE) in Stranski-Krastanov mode at 480℃ and then at the same temperature the pulsed laser was in situ introduced to modify the QDs with different energy. The dependence of morphology evolution on irradiation energy was carefully studied by AFM testing. The results show that laser excitation can enable both desorption and diffusion of In atoms which may induce strong modification on the InAs QDs. For irradiation of a moderate energy, the 3D dot-like InAs QD will transform into 2D oval-shaped island; Once the irradiation energy is high enough, the InAs QDs will be completely removed off from the surface. The involved mechanism is also discussed. Herein, we have proposed a new approach of fabricating QDs which is high-efficient, pollution-free, oxidation-free and defect-resistant and it is believed in the near future, it may find wide applications in both the fundamental physics research and emerging device manufacture.
In this paper, we report the study on the size regulation of Ga-droplets by in situ laser irradiation. Gallium (Ga) droplets are grown on GaAs (001) substrate by molecular beam epitaxy (MBE) and the in situ laser irradiation is carried out by using an ultraviolet pulsed laser. The results show that: The laser irradiation will cause the expansion of Ga-droplets and then the adjacent Ga-droplets can touch with each other and larger Ga-droplets can be formed by the fusion of two or more droplets. So the size of Ga-droplets can be re-modified by laser irradiation and such modification is positively correlated with the irradiation intensity. In other words, we can easily define the size of Ga-droplets by using different laser irradiation energy.