GROWTH-MECHANISM OF GAAS ON (110) GAAS STUDIED BY HIGH-ENERGY ELECTRON-DIFFRACTION AND ATOMIC-FORCE MICROSCOPY

Using in situ reflection high-energy electron diffraction (RHEED) and ex situ atomic force microscopy (AFM) we have studied the homoepitaxial growth on the (110) surface of GaAs. RHEED intensity oscillations indicate a layer-by-layer growth mode. The RHEED intensity oscillation frequency, however, decreases at a constant Ga flux with increasing substrate temperature and decreasing As flux, resulting in a lower apparent growth rate. AFM images of the surfaces reveal that at low As pressures large triangular shaped islands that ultimately lead to a rough surface are formed. The size and height of the islands increase and their density decreases with decreasing As pressures. In the area between the islands up to 1 mum large islands and terraces of monolayer height are found. The AFM images indicate that growth via step-propagation on the islands and the monolayer stepped areas between the islands, not contributing to RHEED intensity oscillations, can account for the decrease in the apparent growth rate. For very low growth rates surface roughening due to island formation during growth is completely suppressed, resulting in a well ordered terraced surface with monolayer high steps and up to 0.5 mum large terraces that are due only to the unintentional 0.04-degrees misorientation of the substrates. The formation of these large terrace sizes is due to the surprisingly large diffusion length of the Ga on the (110) surface.