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.
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.
In this work, surface modification of InAs wetting layer was carried out during InAs/GaAs (001) quantum dot molecular beam epitaxy growth by in-situ pulsed laser (355 nm/ 10 ns). We investigated the morphology transformation of wetting layer by atomic force microscope. Atomic layer removal and formation of nano holes were observed on the sample surface. It is proposed that the material removal of wetting layer induced by electronic excitation is triggered by In atom vacancies due to the desorption at substrate temperature of 480°C. The effects of surface modification on QD growth were studied by subsequent InAs deposition after laser irradiation. Preferential nucleation in nano holes were found in the experiments. This study provides a novel technique leading to site-controlled to InAs/GaAs (001) QDs fabrication.
The AFM study of a series of novel nano-structure on in-situ laser irradiating GaAs(001) substrate in molecular beam epitaxy was presented. Nano-hole, nano-island and nano-ring(Chinese ancient copper coin shape) were observed after laser irradiating. The desorption of Gallium on GaAs surface varies according to different power energy and pulse numbers, leading to the formation of nano-holes, nano-islands and nano-rings. It is speculated that these nanostructures are galliumrich through the change of the RHEED stripe. What’s more, the desorption of defectless GaAs sub-monolayer was discovered, and matched dynamic evolution model (self-drilling effect dominated by Ga atom) was presented. The dependence of the temperature on the surface of the substrate with time was studied after laser irradiating according to the heat conduction equation. The drastic temperature changes caused non-thermodynamic equilibrium process which makes these morphologies.