Potential energy surface of In and Ga adatoms above the (111)A and (110) surfaces of a GaAs nanopillar

Density-functional calculations of the potential-energy surface for tracer Ga and In adatoms above two GaAs (111)A and two GaAs (110) surface reconstructions are presented in order to understand the growth conditions required to form axial GaAs/InGaAs heterostructures in nanopillars. The surface reconstructions present under As-rich conditions have lower diffusion barriers for In adatoms. In addition, the binding energy of In becomes more competitive with Ga under As-rich conditions. We conclude that the As-rich reconstructions for GaAs(110) and GaAs(111)A are preferable for selective formation of heterointerfaces on (111) facets. This work helps explain the recent successful formation of axial GaAs/InGaAs heterointerfaces in catalyst free nanopillars.

Figure 1

(a) SEM of GaAs nanopillars containing axial InGaAs inserts grown at high V/III ratio. (b) Dark-field STEM of single InGaAs insert. (c) SEM of GaAs nanopillars terminated with InGaAs at low V/III ratio.

Figure 2

Surface reconstructions/relaxations of the GaAs (111)A and (110) surfaces. Top left: the (111)A Ga vacancy surface. Top right: the (111)A As trimer surface. Bottom left: the (110) Ga-As chain surface. Bottom right: the (110)As-As chain surface. Arsenic atoms are light gray spheres and gallium atoms are dark gray spheres. Top and side views are rendered with two or three layers of atoms. The atomic diameters are drawn larger for atoms closer to the surface. The unit cell is identified by a shaded parallelogram or rectangle.

Figure 3

Potential energy surface for Ga and In adatoms above the Ga vacancy surface and the As trimer surface (b). The top atomic layers of the reconstruction are drawn as an overlay to assist in visualizing the adsorption sites.

Figure 4

Potential energy surface for Ga and In adatoms above the Ga-As chain surface (a) and the As-As chain surface (b). The top atomic layers of the reconstruction are drawn as an overlay to assist in visualizing the adsorption and transition sites. The primary and secondary adsorption sites are $A_1$ and $A_2$, and the primary and secondary transition points are $T$ and $T^{\prime }$.