Thin film epitaxy using mass selected hyperthermal ions
An energy and mass selected ion beam assisted deposition setup is applied to investigate the influence of hyperthermal atomic and molecular nitrogen ion species during the initial stages of epitaxial GaN thin film growth. Utilizing a compact and versatile quadrupole mass filter system, ions with kinetic energies of up to 200 eV can be extracted from both plasma and ion sources at sufficient efficiency that ion-assisted thin film deposition is viable. The distinct impact of the different ion species on the early stages of GaN thin film growth are elucidated while varying the ion-to-atom arrival ratio and the kinetic energies between 40 eV and 80 eV.
It is determined that precise selection of ion beam parameters enables the preferred growth of either the metastable zinc blende or the stable wurtzite GaN phase on 6H-SiC(0001) substrates. Further, using molecular nitrogen ion species thin films of high crystalline quality could be deposited even at ion kinetic energies of 80 eV, while films with atomic nitrogen ion assistance feature reduced crystalline quality. Additionally, films deposited under molecular nitrogen ion assistance demonstrated a narrower height distribution of domains, indicating a more pronounced two-dimensional nature of the growth.