Kinetic-energy induced smoothening and delay of epitaxial breakdown in pulsed-laser deposition

We have isolated the effect of kinetic energy of depositing species during pulsed laser deposition (PLD) on surface morphology evolution of Ge(001) homoepitaxy at low temperature (100 °C). Using a dual molecular beam epitaxy (MBE)-PLD chamber, we compare morphology evolution from three different growth methods under identical experimental conditions except for the differing nature of the depositing flux: (a) PLD with average kinetic energy 300 eV (PLD-KE); (b) PLD with suppressed kinetic energy comparable to thermal evaporation energy (PLD-TH); and (c) MBE. The thicknesses at which epitaxial breakdown occurs are ranked in the order PLD-KE > MBE > PLD-TH; additionally, the surface is smoother in PLD-KE than in MBE. The surface roughness of the films grown by PLD-TH cannot be compared due to the early epitaxial breakdown. These results convincingly demonstrate that the enhancement of epitaxial growth - the reduction in roughness and the delay of epitaxial breakdown - are due to the high kinetic energy of depositing species in PLD.