UV-Induced Negative Growth of In Nanodroplets and Mounds from Ultrathin In Layers on Sublimated InP(110)

Ultrathin In layers formed on InP(110) by vacuum sublimation act as reservoirs that, during cooling and simultaneous exposure to ultraviolet (UV) photons, grow into different nanostructures depending on the conductivity type of the underlying semiconductor. In situ observation by synchrotron-based spectroscopic low-energy electron microscopy shows that on n-type InP(110), the ultrathin layers grow into two-dimensional (2D) islands or mounds only. On p-type InP(110), similar 2D mounds also exist, but they are decorated by nanoscale droplets, indicating a Stranski–Krastanow growth mode. The effects that UV exposure has on the ultrathin In layers are optomechanical in nature as induced quantum electronic stress results in partial decoupling of the layers from the semiconductor surface, driving the released atoms to minimize their energies by forming conductivity type-dependent stable configurations. Semiconductor surfaces with different conductivity types have different workfunctions or, equivalently, different chemical potentials for adatoms, which provide the physical origin of the observed different morphologies of In on InP. The results provide an experimental proof that the conductivity type of substrates/supports could influence the final morphologies and thus properties of the overgrown metal structures. Consequently, strategies could be devised to ensure flat, ultrathin metallic or even superconducting films of technological and fundamental interests.