Effects of substrate orientation and surface reconstruction on patterned substrate OMVPE of GaAs

Organometallic vapor phase epitaxial growth of GaAs on 320 nm high mesas wa s used to study the dependence of lateral growth upon the substrate misorie ntation fi om (100) and the mesa wall orientation on the substrate. GaAs (1 00) substrates were misoriented by 3 degrees toward eight major crystallogr aphic directions, consisting of the four nearest [111] and [110] directions . The mesa sidewalls were oriented either parallel to the <011> and <01(1) over bar> directions or rotated by 45 degrees to be parallel to the <001> a nd <010> directions. GaAs films were grown with TMGa and TEA at T = 575C de grees. The lateral growth rates were up to 25 times higher than the vertica l growth rate of 1.3 mu m/hour. Optical microscopy and atomic force microsc opy (AFM) showed that under the given growth conditions lateral growth off mesa sidewalls is most rapid in the <011> and/or <011> directions and less in the perpendicular <01(1) over bar> and <0(1) over bar 1> directions (lat eral growth anisotropy). By raising the temperature to 625 degrees C latera l growth in the <01(1) over bar> - <0(1) over bar 1> directions Increased w hile it remained almost constant in the <011> - <<0(11)over bar >> directio ns. Published results show that the partial pressure of As also affects lat eral growth. Differences in the lateral growth rates in the <011> and its o pposite <<0(11)over bar >> directions result from substrate misorientation but not from the orientation of the mesa walls on the substrate. Anisotropi c lateral growth rates in different crystallographic directions appear to b e caused by both, (1) 1-dimensional Ga diffusion defined by surface reconst ruction, and (2) a relatively low energy barrier to atoms flowing over high -to-low terrace steps. A lateral growth model is proposed that describes an isotropic lateral growth at mesa sidewalls in terms of growth conditions an d substrate misorientations. The model also explains the difference in the preferential lateral growth directions between MBE and OMVPE.