Formation of GaPd2 and GaPd intermetallic compounds on GaN(0001)

Abstract

Palladium was deposited gradually under ultrahigh vacuum onto a well-defined surface of (0001)-oriented n-type GaN, at room temperature. Each deposition step was followed by annealing. Physicochemical properties of the Pd adlayers were in situ investigated prior to and after annealing by the X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, low-energy electron diffraction, scanning tunneling microscopy and atomic force microscopy techniques. Annealing resulted in the formation of GaPd 2 and GaPd intermetallic compounds at 550°C and at 800°C. Even for thicker layers, the compounds were strongly dispersed, forming 3D nanostructures. The substrate uncovered by the compounds revealed Ga-rich GaN(0001)-(1 9 1) surface. Formation of Ga-Pd-N bonds or Pd nitrides was not detected at the surface. The Ga-Pd intermetallic compound surface engineered on the GaN(0001) substrate can be used as the strongly dispersed catalyst or a model catalyst.

Studies of early stages of Mn/GaN(0001) interface formation using surface-sensitive techniques

“…The valence band edge is located 17.6 eV above the Ga-3d core level. The value is in good agreement with those reported in our previous papers and other works [19][20][21][22][23][24] and indicates that the is accounted to be 4.2 eV and was calculated using the basic formula WF = hv -Ecutoff. The UPS measurements allow us to understand the band structure of the substrate, a common effect, which manifests at the semiconductor surface as band bending (BB).…”

Modification of Electronic Structure of n-GaN(0001) Surface by N+-Ion Bombardment

“…The electron affinity χ of the clean surface calculated basing on the relationship χ = hν − W − E g amounts to 3.4 eV, where hν = 21.2 eV is the photon energy of He(I); the spectrum width W is the energy difference between the V BM and the cutoff energy of photoemission, equal to 14.4 eV; and E g is the width of the GaN band gap assumed to be equal to 3.4 eV. The V BM lies 17.7 eV above the Ga 3d core level, which is in agreement with the value reported in our previous paper on the formation of Ga-Pd intermetallic compounds at Pd/GaN(0001) interface [6]. The valence band changes under the N + ion bombardment; the positions of the cutoff energy and the V BM are shifted.…”

Properties of Thin Film-Covered GaN(0001) Surfaces

“…The interfacial reaction between nickel and GaN can occur during annealing [33], which is a commonly used step for contact creation. This can lead to the formation of new Ni-Ga alloys, similarly to the case of the Pd/GaN interface [34], that have catalytic potential [35][36][37][38][39][40][41]. In addition to metals, another interesting group of materials deposited as thin layers on GaN surfaces are semi-metals, such as arsenic (As) and antimony (Sb).…”

“…This is, among other things, due to: (i) the relatively difficult cleaning procedure of the GaN surface, which may lead to changes in its stoichiometry. The bare and metal-covered surface can easily be enriched with gallium [29,34,62], which can lead to a bad interpretation of the deconvoluted Ga-3d components; (ii) the presence of a large number of Ga Auger lines which may overlap others' core level spectra; and (iii) surface photovoltage (SPV) effects which can cause changes in the Fermi level position versus the valence band maximum [63,64]. Furthermore, SVP can sometimes even lead to the appearance of a quasar Fermi level in the metal/GaN system [30], which can be mistakenly interpreted as a chemical shift.…”