SURFACE-TOPOGRAPHY AND ORDERING-VARIANT SEGREGATION IN GALNP2

Using transmission electron diffraction dark-field imaging, atomic force microscopy (AFM), and Nomarski microscopy, we demonstrate a direct connection between surface topography and cation site ordering in GaInP2. We study epilayers grown by organometallic vapor-phase epitaxy on GaAs substrates oriented 2-degrees off ( 100) towards (110). Nomarski microscopy shows that, as growth proceeds, the surface of ordered material forms faceted structures aligned roughly along [011]. A comparison with the dark-field demonstrates that the [111BAR] and [111BAR] ordering variants are segregated into complementary regions corresponding to opposite-facing facets of the surface structures. This observation cannot be rationalized with the obvious but naive model of the surface topography as being due to faceting into low-index planes. However, AFM reveals that the facets are in fact not low-index planes, but rather are tilted 4-degrees from (100) towards (111) B. This observation explains the segregation of the variants: the surface facets act as local (111) B-misoriented growth surfaces which select only one of the two variants.