Evolution of surface morphology on compound semiconductor surfaces by ion erosion has become an important area of research. However, knowledge on the effects of experimental parameters such as ion flux/current density, ion fluence, angle of incidence of the ion, and surface crystallographic orientation of the sample becomes crucial to optimize the process of formation self-organized nanostructures. We have chosen GaAs for its applications in opto-electronic devices based on arrays of nanostructures such as quantum dots. Nanodot formation has been reported on GaAs surfaces using 50-60 keV Ar⁺-ion sputtering but along with hole/pit [1] and ripple formation [2]. Nanodots with pits were observed in n-GaAs(100) for normal incidence [1], while dots on ripples were formed in case of semi-insulating (SI)-GaAs(100) for 60° off-normal incidence [2]. In this work, we implanted 60 keV Ar⁺-ions in p- GaAs(100) by using a current density of ~10-12 μA/cm² for incident angles between 0°-60° and fluences (2×10¹⁷-3×10¹⁸ ions cm^-2). Atomic force microscopic (AFM) studies indicate formation of nanodots (26-40 nm) without any short range ordering for 60° off-normal incidence. The largest dots are smaller by a factor of 3, as compared to the smallest dots reported in [2] on SI-GaAs(100). There is no ripple formation even at the highest fluence (3×10¹⁸ ions cm^-2).

References

[1] S. K. Mohanta, R. K. Soni, N. Gosvami, S. Tripathy, D. Kanjilal, Appl. Surf. Sci., 253 (2007) 4531.

[2] D. Datta, S. R. Bhattacharyya, T. K. Chini, M. K. Sanyal, Nucl. Inst. and Meth. in Phys. Res. B, 193  (2002) 596.