Structural properties of GaN layers on Si(001) grown by plasma-assisted molecular beam epitaxy

We report on the growth and microstructure of GaN films deposited on Si(001) substrates by plasma-assisted molecular beam epitaxy, GaN films grown directly on Si(001) are found to be phase mixtured, containing both cubic (beta) and hexagonal (alpha) modifications. The origin of this phase mixture is identified to be due to the formation of amorphous SixNy at the GaN/Si interface during the nucleation stage. Therefore, a GaAs buffer layer is employed to prevent the formation of SixNy. GaN films grown on this GaAs/Si(001) structure are in fact predominantly cubic and exhibit the characteristic band-edge photoluminescence (PL) of beta-GaN up to room temperature. However, the. PL efficiency from these samples is lent compared to that of beta-GaN layers directly grown on GaAs(001). We explain the lower PL efficiency by the presence of additional structural defects, which are observed in the GaN/GaAs/Si(001) heterostructure by transmission electron microscopy. (C) 1998 American Institute of Physics. [S0021-8979(98)05907-6].