Potential energy threshold of surface erosion on GaN by impact of slow highly charged heavy ions

In the present work the erosion behavior on the surface of GaN epi-layer by the impact of various slow highly charged heavy ions (SHCIs, including Ar^q+, Xe^q+ and Pb^q+, in two incidence geometries) was investigated. Atomic force microscopy reveals a well-defined threshold of potential energy carried by the incident heavy ions accounting for the surface erosion. This threshold also depends on the projected range of the SHCIs, the longer the projected range, the higher the potential energy required for the onset of surface erosion. And the etched depth is close to a linear function of potential energy deposited, increasing with the potential energy increases. Moreover, the etching rate for 60° off normal incidence is by more than a factor of 2 larger than etching rate for normal incidence, and the etch rate by Xe^q+ is larger than by Pb^q+ under the same potential energy and incident direction. And a mechanism is discussed.