Theoretical analysis of initial adsorption of high-κ metal oxides on InxGa1−xAs(  1)-(4×2) surfaces

Abstract

Ordered, low coverage to monolayer, high-κ oxide adsorption on group III rich InAs(0 0 1)-(4×2) and In(0.53)Ga(0.47)As(0 0 1)-(4×2) was modeled via density functional theory (DFT). Initial adsorption of HfO(2) and ZrO(2) was found to remove dangling bonds on the clean surface. At full monolayer coverage, the oxide-semiconductor bonds restore the substrate surface atoms to a more bulklike bonding structure via covalent bonding, with the potential for an unpinned interface. DFT models of ordered HfO(2)/In(0.53)Ga(0.47)As(0 0 1)-(4×2) show it fully unpins the Fermi level.

Initiation of a passivated interface between hafnium oxide and In(Ga)As( 1)−(4×2)

“…Theoretical results in the companion paper further support that the fortuitous structure of HfO 2 allows for the elimination of the partially filled dangling bonds on the surface by formation of both Hf-As bonds and O-In/Ga bonds. 33…”

“…These specific chemisorption sites have been modeled using density functional theory ͑DFT͒, and those results are published in a companion paper. 33 In that paper, DFT results reveal that the double HfO 2 bridge site is slightly more stable than the single HfO 2 half-bridge "row edge" site by about 0.4 eV/ HfO 2 molecule. This is consistent with the STM results, showing the population of bridge sites is larger than one would expect by a random distribution of single sites.…”

“…In STM images, single HfO 2 sites appear different than the single Hf atom sites--the HfO 2 sites are slightly larger in diameter and higher above the row. The DFT calculations of Bishop et al 33 show that the lowest energy bonding structure for a HfO 2 molecule is for it to be oriented over the trough region, along the side of the row via O-In bonds and Hf-As bonds. This bonding configuration is illustrated in the ball and stick diagram of the half-bridge row-edge site in Fig.…”

“…5͑b͒ suggests that the HfO 2 bonds to the III-V substrate are relatively weak; the diffusion of HfO 2 on the surface to form these ordered regions would not be likely to occur for this refractory oxide if the bonds to the substrate were strong. DFT calculations by Bishop et al 33 show that the chemisorption energy of the HfO 2 molecule to the III-V surface is 3.95-4.34 eV, which corresponds to only ϳ1.4 eV per bond since the HfO 2 makes three bonds to the surface. STS was performed on full-coverage HfO 2 / InGaAs͑0 0 1͒ − ͑4 ϫ 2͒ for both p-type and n-type substrates and compared to STS results for the clean InGaAs͑0 0 1͒ − ͑4 ϫ 2͒ surfaces.…”

“…27,39 For HfO 2 / InGaAs͑1 0 0͒ − ͑4 ϫ 2͒, the interfacial bonds are not bulklike; instead they are Hf-As bonds and O-In/Ga bonds. 33 Strong highly ionic bonds are expected to create midgap states which pin the interface, but this does not occur for HfO 2 / InGaAs͑0 0 1͒ − ͑4 ϫ 2͒. Instead the bonds are relatively weak, as shown by the formation of some locally ordered regions at medium coverage.…”