Electron spectro-microscopic determination of barrier height and spatial distribution of Au and Ag Schottky junctions on boron-doped diamond (001)

Abstract

Electron spectro-microscopic methods were applied as direct methods of determining the Schottky barrier heights (SBHs) and their spatial distribution for Au-and Ag-Schottky junctions fabricated on an acid-treated oxygen-terminated diamond (001) substrate. Metal layers were formed with two ranges of thickness (3-5 nm for thin layers and 13-100 nm for thick layers) for both Au-and Ag-Schottky junctions. Leading X-ray photoelectron spectroscopy (XPS) core-level peaks of either Au 4f 7/2 or Ag 3d 5/2 for the metal layers and C 1s for diamond were used as measures of the SBH. For the thick-metal samples, spatially resolved XPS measurements were performed over most of the sample surface. It was found that there is a variation in SBH on the order of 0.1 eV for the large ("high barrier") SBH values and that there are several places where the SBHs were rather small ("low barrier" junction). For the thin-metal samples, less variations in SBH were observed. The average SBH of "high barrier" junctions for the thick-metal samples appeared to be slightly (0.1 eV order) larger than that for the thin-metal samples. XPS images of leading metal core levels tuned for the "high barrier" and "low barrier" SBHs were observed. For the thick-Ag Schottky sample, the resulting Ag 3d 5/2 XPS images clearly showed the locations of defective Schottly junctions. It is suggested that the SBHs determined for the thin-metal samples are the average SBHs on the measured surface and that the SBHs determined for the thick-metal samples are the highest SBHs within the measured µm-size metal islands. The presently determined SBHs were compared with previously reported SBHs and reasonable agreement was found. Photoemission electron microscopy (PEEM) images were observed for the thick-Ag Schottky sample and the "low barrier" islands were identified. The methodologies of XPS, XPS imaging, and PEEM used for the thick-metal samples can be applied to any Schottky junction on diamond.

Imaging of diamond defect sites by electron-beam-induced current

“…OM images as examined by the Raman-spectrometer at a magnification of 20 times showed a smooth appearance except for some parts. X-ray photoelectron spectra (XPS) of the sample showed~1.5 monolayer of oxygen on the surface with effectively no other impurities, which was similar to the previous XPS results [24]. For the EBIC measurements, the Ag-layer of~50 nm thick (as estimated from the deposition rate and duration) was deposited from an alumina crucible heated by W filament at a vacuum of~10 −7 Torr.…”

“…Then Ag-dots (thickness of~70 nm) of a rectangle size of~40 × 50 μm 2 were deposited over the entire sample area through a #300 (300 divisions per inch) mesh in the same vacuum chamber used for the Ag-layer deposition for the EBIC. For 53 Ag-dots in an area corresponding to EBIC observation, I-V characteristics were measured in a vacuum of~10 −5 Torr, and SBHs and ideality factors of Schottky junctions were evaluated as previously [24]. SBHs of the Ag-dots were directly determined by XPS as was performed previously [24].…”

“…Schottky junction metals other than Ag may also be used in the present EBIC although SBH of Ag junction is one of the largest [24]. In principle, this EBIC method can be applied to n-type diamond samples but the polarity of current would be reversed.…”

“…1b) shows a schematic energy band diagram at the Schottky junction, where E V and E C denote the valence band top and conduction band bottom of the boron-doped diamond, respectively, and E F denotes the Fermi level. The Schottky barrier height (SBH or ϕ SB ) of good Ag Schottky layers on the oxidized diamond (001) surface is determined to be~1.9 eV [24]. The SBHs at defective sites (possible 'killer' defect sites) are found to be substantially lower [24].…”

“…The Schottky barrier height (SBH or ϕ SB ) of good Ag Schottky layers on the oxidized diamond (001) surface is determined to be~1.9 eV [24]. The SBHs at defective sites (possible 'killer' defect sites) are found to be substantially lower [24].…”