The effects of mask openings on the selective liquid-phase epitaxial growth of GaAs microtips

We investigate the effects of the shape and orientation of mask openings on selective liquid-phase epitaxial growth of GaAs microtips. Five kinds of mask openings have been designed for this study. First one is a square opening with the four sides parallel to the 〈1 1 0〉 directions. The second is also a square opening, but with the four sides parallel to the 〈1 0 0〉 directions, namely the directions having an angle of 45° relative to the 〈1 1 0〉 directions. The third is an equilateral triangle opening with one side parallel to [1 1 0] direction. The fourth is a rectangular opening with the four sides parallel to the 〈1 1 0〉 directions. The last one is a round opening. Scanning electron microscopy (SEM) is employed to characterize the GaAs microtips. The results indicate that the pyramidal microtips bounded by four {1 1 1} planes are always formed under all of the five situations, and the shapes of the microtip tops are either pointed or edged. This means that the growth of the microtip is independent of the shape and orientation of the mask openings. But the ratio of the two maximum sizes of an opening along the [1 1 0] and [1 1¯ 0] directions dominates the top shape of a microtip. A preliminary explanation is also given in this paper.