Atomic imaging and modeling of H2O2(g) surface passivation, functionalization, and atomic layer deposition nucleation on the Ge(100) surface.

Passivation, functionalization, and atomic layer deposition nucleation via H2O2(g) and trimethylaluminum (TMA) dosing was studied on the clean Ge(100) surface at the atomic level using scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). Chemical analysis of the surface was performed using x-ray photoelectron spectroscopy, while the bonding of the precursors to the substrate was modeled with density functional theory (DFT). At room temperature, a saturation dose of H2O2(g) produces a monolayer of a mixture of -OH or -O species bonded to the surface. STS confirms that H2O2(g) dosing eliminates half-filled dangling bonds on the clean Ge(100) surface. Saturation of the H2O2(g) dosed Ge(100) surface with TMA followed by a 200 °C anneal produces an ordered monolayer of thermally stable Ge-O-Al bonds. DFT models and STM simulations provide a consistent model of the bonding configuration of the H2O2(g) and TMA dosed surfaces. STS verifies the TMA/H2O2/Ge surface has an unpinned Fermi level with no states in the bandgap demonstrating the ability of a Ge-O-Al monolayer to serve as an ideal template for further high-k deposition.

Density functional theory simulations of amorphous high-κ oxides on a compound semiconductor alloy: a-Al2O3/InGaAs(100)-(4×2), a-HfO2/InGaAs(100)-(4×2), and a-ZrO2/InGaAs(100)-(4×2).

The structural properties of a-Al(2)O(3)∕In(0.5)Ga(0.5)As, a-HfO(2)∕In(0.5)Ga(0.5)As, and a-ZrO(2)∕In(0.5)Ga(0.5)As interfaces were investigated by density-functional theory (DFT) molecular dynamics (MD) simulations. Realistic amorphous a-Al(2)O(3), a-HfO(2), and a-ZrO(2) samples were generated using a hybrid classical-DFT MD "melt-and-quench" approach and tested against the experimental properties. For each stack type, two systems with different initial oxide cuts at the interfaces were investigated. All stacks were free of midgap states, but some had band-edge states which decreased the bandgaps by 0%-40%. The band-edge states were mainly produced by deformation, intermixing, and bond-breaking, thereby creating improperly bonded semiconductor atoms. The interfaces were dominated by metal-As and O-In∕Ga bonds which passivated the clean surface dangling bonds. The valence band-edge states were mainly localized at improperly bonded As atoms, while conduction band-edge states were mainly localized at improperly bonded In and Ga atoms. The DFT-MD simulations show that electronically passive interfaces can be formed between high-κ oxides dielectrics and InGaAs if the processing does not induce defects because on a short time scale the interface spontaneously forms electrically passive bonds as opposed to bonds with midgap states.

Scanning tunneling microscopy/spectroscopy study of atomic and electronic structures of In2O on InAs and In0.53Ga0.47As(001)-(4×2) surfaces.

Interfacial bonding geometry and electronic structures of In(2)O on InAs and In(0.53)Ga(0.47)As(001)-(4×2) have been investigated by scanning tunneling microscopy/scanning tunneling spectroscopy (STM/STS). STM images show that the In(2)O forms an ordered monolayer on both InAs and InGaAs surfaces. In(2)O deposition on the InAs(001)-(4×2) surface does not displace any surface atoms during both room temperature deposition and postdeposition annealing. Oxygen atoms from In(2)O molecules bond with trough In/Ga atoms on the surface to form a new layer of O-In/Ga bonds, which restore many of the strained trough In/Ga atoms into more bulklike tetrahedral sp(3) bonding environments. STS reveals that for both p-type and n-type clean In(0.53)Ga(0.47)As(001)-(4×2) surfaces, the Fermi level resides near the valence band maximum (VBM); however, after In(2)O deposition and postdeposition annealings, the Fermi level position is close to the VBM for p-type samples and close to the conduction band minimum for n-type samples. This result indicates that In(2)O bonding eliminates surface states within the bandgap and forms an unpinned interface when bonding with In(0.53)Ga(0.47)As/InP(001)-(4×2). Density function theory is used to confirm the experimental finding.

Theoretical analysis of initial adsorption of high-κ metal oxides on In(x)Ga(1-x)As(0 0 1)-(4×2) surfaces.

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.

Atomic imaging of the monolayer nucleation and unpinning of a compound semiconductor surface during atomic layer deposition.

The reaction of trimethyl aluminum on the group III rich reconstructions of InAs(0 0 1) and In(0.53)Ga(0.47)As(0 0 1) is observed with scanning tunneling microscopy/spectroscopy. At high coverage, a self-terminated ordered overlayer is observed that provides the monolayer nucleation density required for subnanometer thick transistor gate oxide scaling and removes the surface Fermi level pinning that is present on the clean InGaAs surface. Density functional theory simulations confirm that an adsorbate-induced reconstruction is the basis of the monolayer nucleation density and passivation.

Ab initio molecular dynamics simulations of properties of a-Al2O3/vacuum and a-ZrO2/vacuum vs a-Al2O3Ge(100)(2 x 1) and a-ZrO2Ge(100)(2 x 1) interfaces.

The local atomic structural properties of a-Al(2)O(3), a-ZrO(2) vacuum/oxide surfaces, and a-Al(2)O(3)Ge(100)(2x1), a-ZrO(2)Ge(100)(2x1) oxide/semiconductor interfaces were investigated by density-functional theory (DFT) molecular dynamics (MD) simulations. Realistic a-Al(2)O(3) and a-ZrO(2) bulk samples were generated using a hybrid classical-DFT MD approach. The interfaces were formed by annealing at 700 and 1100 K with subsequent cooling and relaxation. The a-Al(2)O(3) and a-ZrO(2) vacuum/oxide interfaces have strong oxygen enrichment. The a-Al(2)O(3)Ge interface demonstrates strong chemical selectivity with interface bonding exclusively through Al-O-Ge bonds. The a-ZrO(2)Ge interface has roughly equal number of Zr-O-Ge and O-Zr-Ge bonds. The a-Al(2)O(3)Ge junction creates a much more polar interface, greater deformation in Ge substrate and interface intermixing than a-ZrO(2)Ge consistent with experimental measurements. The differences in semiconductor deformation are consistent with the differences in the relative bulk moduli and angular distribution functions of the two oxides.