Morphological switching in synchrotron-radiation-excited Ge homoepitaxy: Transition from kinetic roughening to smoothing Available to Purchase

The surface morphology of Ge films during $GeH4$-source molecular beam epitaxy on a Ge(100) substrate is dramatically changed through irradiation with synchrotron radiation $(hν>100eV)$⁠. At temperatures below 300 °C, a two-dimensionally flat film continues to grow with the surface tightly passivated by a $GeHx$ hydride layer. At temperatures above 350 °C, dangling bonds are partially terminated with hydrogen atoms while Ge adatoms are highly mobile, resulting in a nonuniform nucleation that creates the islands. Small islands merge into a few-hundred-nanometer-tall islands surrounded by the (113)-face sidewalls. This kinetic roughening continues until the nucleation on the (001) plane ceases due to the buildup of the $GeHx$ layer. Once the surface free energy is minimized by the hydrogen termination, flattening of the islands proceeds to reduce the chemical potential of the system. The valleys between the islands are preferentially filled, and the film is eventually converted into a smooth epilayer with no memory of the initial roughening.