The electronic and chemical structure of the a-B₃CO_0.5:H_y-to-metal interface from photoemission spectroscopy: implications for Schottky barrier heights

Abstract

The electronic and chemical structure of the metal-to-semiconductor interface was studied by photoemission spectroscopy for evaporated Cr, Ti, Al and Cu overlayers on sputter-cleaned as-deposited and thermally treated thin films of amorphous hydrogenated boron carbide (a-B(x)C:H(y)) grown by plasma-enhanced chemical vapor deposition. The films were found to contain ~10% oxygen in the bulk and to have approximate bulk stoichiometries of a-B(3)CO(0.5):H(y). Measured work functions of 4.7/4.5 eV and valence band maxima to Fermi level energy gaps of 0.80/0.66 eV for the films (as-deposited/thermally treated) led to predicted Schottky barrier heights of 1.0/0.7 eV for Cr, 1.2/0.9 eV for Ti, 1.2/0.9 eV for Al, and 0.9/0.6 eV for Cu. The Cr interface was found to contain a thick partial metal oxide layer, dominated by the wide-bandgap semiconductor Cr(2)O(3), expected to lead to an increased Schottky barrier at the junction and the formation of a space-charge region in the a-B(3)CO(0.5):H (y) layer. Analysis of the Ti interface revealed a thick layer of metal oxide, comprising metallic TiO and Ti (2)O (3), expected to decrease the barrier height. A thinner, insulating Al(2)O(3) layer was observed at the Al-to-a-B(3)CO(0.5):H(y) interface, expected to lead to tunnel junction behavior. Finally, no metal oxides or other new chemical species were evident at the Cu-to-a-B(3)CO(0.5):H(y) interface in either the core level or valence band photoemission spectra, wherein characteristic metallic Cu features were observed at very thin overlayer coverages. These results highlight the importance of thin-film bulk oxygen content on the metal-to-semiconductor junction character as well as the use of Cu as a potential Ohmic contact material for amorphous hydrogenated boron carbide semiconductor devices such as high-efficiency direct-conversion solid-state neutron detectors.

Topological Constraint Theory Analysis of Rigidity Transition in Highly Coordinate Amorphous Hydrogenated Boron Carbide

“…Hydrogen is known to exhibit rare bridging B-H-B bonding in amorphous boron-based solids (Anan'ev et al, 2002), but since this is not observed spectroscopically, we assume its contribution is absent or negligible. Finally, we would be remiss to not mention oxygen, which is inevitably present in these a-BC:H films in concentrations ranging from ∼1-10% (Driver et al, 2012;Nordell et al, 2015). This element is found to exist in the form of OH groups, CO groups, and/or boron-oxide-based species, and is generally considered 2-fold coordinate.…”

Improved p–n heterojunction device performance induced by irradiation in amorphous boron carbide films

“…synthesized by CVD and PECVD are wide ranging [8,44,45]. This is represented by a-B 10 C 2+x :H y with 0 < x < 3 and 0 < y <12.…”

Strong binding at the gold (Au) boron carbide interface

“…Semiconductor boron carbides have been shown to be suitable for semiconducting devices and solid state neutron detection [11][12][13][14][15][16][17][18][19][20][21][22][23]. Essential to any semiconductor device is the metal contact and the chemical interactions or band bending that may occur at the metal/semiconductor interface, so increasingly there has been investigation of the interface of various boron carbides to various metals [24][25][26][27]. Understanding the metal contacts on the surface of these semiconductors presents a number of important challenges.…”

“…As such, a fairly unreactive large work function metal contact, such as Au (with a work function in the range of 5.3 to 5.5 eV [31][32][33]) or Pt (with a work function in the range of 5.6 to 5.9 eV [33,34]), would be expected to form a Schottky barrier contact. Low work function metals have attracted much attention, but are often seen to be quite reactive at the interface with boron carbide [24]. A less reactive metal, with high work function, is an important juxtaposition, and may afford insight as to whether the formation of Schottky barrier contacts with PECVD hydrogenated semiconducting boron carbide is facile.…”