Recently, it has been reported, through using an in-situ laser exposure, nano holed structures can be created on the GaAs surface that is pre-capped by a thin InAs wetting layer and such nano holes were further proven to well serve as the preferential nucleation sites of InAs quantum dots (QDs). In this paper, we presented a study of how to further modify the morphology of the nano holes. First homo-deposition of 500nm GaAs buffer layer on GaAs (100) substrate and after capping of 0.5ML InAs, the as-prepared surface was in-situ exposed by a laser shot with energy of 20mJ. Then four different samples (A-D) were prepared, respectively corresponding to directly finishing the growth for sample A, for sample B repeating one cycle of “0.3ML InAs wetting layer capping + in situ laser exposure” before finishing the whole growth, two cycles for sample C and three cycles for sample D. It is found the density of nano holes on sample A is merely 5.5×108/cm2 with relatively small size possessing an average depth and width at 0.9nm and 36.6nm. After one cycle of “0.3ML InAs wetting layer capping + in situ laser exposure”, the density of nano holes on sample B increases by nearly one order of magnitude to 4.33×109/cm2 and the average depth and width become 1.0nm and 44.6nm. Further after two and three cycles, the resulting density would rise to 8.53 × 109/cm2 (sample C) and 1.12 × 1010/cm2 (sample D), correspondingly, the average depth/width are magnified to 1.1nm/54.2nm and 1.3nm/59.7nm. Hence, we have demonstrated an effective approach to modify the in-situ laser nano-holed patterning of GaAs surface which is supposed to have promising applications in controlled growth of QDs.
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, 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.
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.
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