Scanning tunneling microscopy has been used to examine growth mode of Al on a Si (111) (√3×√3) -Alsurface at room temperature. It is found that submonolayer deposition leads to formation of tiny 2 dimensional (2D) nuclei of Al. These nuclei are uniformly distributed over Si (111) (√3×√3) -Al terraces. When increasing a coverage of 5 monolayers, tiny Al 2D nuclei coalesce to form large Al islands with atomically flat (111) surfaces. We will discuss the difference in growth mode in terms of Al diffusion length.
A two-step atomic-hydrogen (atomic-H) treatment of GaAs substrate was investigated; this includes low-temperature cleaning and high-temperature smoothening of GaAs (001) substrate surface. It was found that atomically flat GaAs surface with one monolayer-height steps and ragged step edges could be obtained by the atomic-H treatment at high temperatures. Further, growth of high quality cubic GaN (c-GaN) on atomic-H treated GaAs (001) was examined by rf plasma-assisted MBE. The c-GaN epilayers were characterized by high resolution X-ray diffraction analysis. The results show that the FWHM of the X-ray rocking curve for the (002) c-GaN was as small as 70-90 arcsec and the inclusion of hexagonal GaN phase was about 0.4% (or below). This indicates that the atomic-H irradiation treatment of the GaAs substrate was an efficient method obtaining High quality c-GaN.