Study Of Arsenide Semiconductor Surface By In-situ Pulsed Laser Irradiation In MBE

Arsenide like GaAs hetero-epitaxy devices has been intensively studied due to their important application in optoelectronic, microelectronic, and quantum controlling. Low dimensional quantum structures, Low dimensional quantum structures, especially InAs/GaAs quantum dots(QDs) reveal ideal optoelectronic properties. However, the nucleation of self-organized QDs is non-uniform and uncontrollable. Traditional method to control the growth of QDs is patterning the substrate. While unavoidable defects and impurities largely degrade the materials.We have successfully grown defect-free site-controlled QDs by in-situ laser interference patterning. In this thesis, in-situ nanosecond pulse laser irradiation on GaAs and InAs surfaces was studied in molecular beam epitaxy. Arsenic atoms were selectively desorbed away from GaAs(100) surface by laser irradiation and this lead to the formation of perturbed Ga-rich surface. The Arsenic desorption increased with the energy density, and Ga droplets formed with the increased number of the laser pulses.The reflected high energy electron diffraction showed that surface reconstruction changed from 2×4 to 4×2 with laser irradiation and gradually turned back to 2×4 in Asenic protection environment after the laser irradiation was stopped. The Ga atoms gathered together to form Ga droplets under multiple laser pulses, and the Ga droplets changed to nano-rings during in-situ annealing.InAs wetting-layer was in-situ irradiation with laser pulse during the growth of QDs. Atomic layer removal and 1~3nm of nano-holes of were observed on wetting layer after the irradiation. Laser induced electronic excitation caused the change of surface morphology. Indium atoms on the surface of In As wetting-layer were unstable at high substrate temperature. In the beginning, the sites with the desorption of Indium atoms acted as defects, and then the desorption was amplified rapidly till an atomic layer was removed. The in-situ surface modification affects the QDs growth. The nucleation of QDs were significant delayed because of the atomic layer removal. While nano-holes formed at high laser intensity sites acted as preferential nucleation sites for QDs.