Accurate ab initio determination of ballistic electron emission spectroscopy: Application to Au/Ge

Abstract

Ab initio non-equilibrium Keldysh formalism based on an N-order renormalisation technique is used to compute I(V) Ballistic Electron Emission Microscopy characteristics at the Au/Ge(001) interface. Such a formalism quantitatively reproduces precise experimental measurements under ultra-high vacuum and low-temperature conditions. At T = 0 K the ballistic current follows the law (V − V SB) 2.1 , V SB being the Schottky barrier. At T > 0 K, temperature effects become significant near the onset and must be taken into account to identify an accurate value for V SB from a best-fit procedure. We find two values for V SB : 0.67 and 0.75 eV, which we associate with two different atomic registries at the interface.

Benchmarking β‐Ga2O3 Schottky Diodes by Nanoscale Ballistic Electron Emission Microscopy

“…Concerning (i), the energy band structure of β‐Ga 2 O 3 shows a direct conduction band minimum at the center (Γ) of the Brillouin zone, whereas other conduction band minima are predicted to be at least 2 eV higher. The single threshold of the spectra thus originates—according to the general BEEM theory24,25—from hot electrons injection into the conduction band minimum at the center zone Γ. Regarding (ii), values agree with predictions for the transition level of the doubly ionized fourfold‐coordinated oxygen vacancies (approx.…”

“…The local SBH, ϕ B0 , is then defined by the onset of the collector current in I BEEM versus V T spectra (Figure 1c). Most of the BEEM studies have focused on SBDs involving non‐oxidic semiconductors (e.g., Si, Ge, GaAs, SiC, GaN, ZnSe),24,25 and only recently BEEM succeeded to probe devices based on the perovskite transition metal oxide SrTiO 3 (Nb‐doped, n‐ type) 26–28. Hereafter, we demonstrate that BEEM can effectively investigate SBDs fabricated onto freshly cleaved (100)β‐Ga 2 O 3 single crystal substrates.…”

Macroscopic Versus Microscopic Schottky Barrier Determination at (Au/Pt)/Ge(100): Interfacial Local Modulation

“…31,32 In this paper, we characterize the SBH formed at the M/Ge(100) interface by analyzing BEES measurements in the framework of a recently developed N-order abinitio modelling, which makes possible to treat large enough interfaces to explore more realistic models for the system. 33 Au/Ge(100) contacts have been prepared by depositing under Ultra High Vacuum (UHV) a Au electrode of about 15 nm nominal thickness on atomically flat Ge(100) [34][35][36][37] by Physical Vapour Deposition (PVD), while another set of Schottky junctions were prepared on the same substrate by depositing either Au or Pt by Pulsed Laser Deposition (PLD). Microcospic BEES measurements were performed under UHV at T = 80 K using a modified commercial STM apparatus, and macroscopic two-point Current-Voltage (I-V) measurements were acquired in situ at room temperature, T = 290 K (RT), and at a lower temperature, T = 80 K. work-function metals (namely, Pt and Au), we cut the Ge substrate into pieces of about 10 × 5 × 0.5 mm 3 and cleaned them in ultrasonic baths of acetone (5 min) and 2-propanol (5 min), followed by drying in pure N 2 flow.…”

“…Despite a large number of studies concerning the characterization of metal/germanium SBH by macroscale techniques, a detailed microscopic study by BEES of such an M/Ge interface is missing, even though studies have been published on buried Ge dots and Si 1– x Ge x strained interfaces. , In this paper, we characterize the SBH formed at the M/Ge(100) interface by analyzing BEES measurements in the framework of a recently developed N -order ab initio modeling, which makes possible to treat large enough interfaces to explore more realistic models for the system . Au/Ge(100) contacts have been prepared by depositing under ultra high vacuum (UHV) an Au electrode of about 15 nm nominal thickness on atomically flat Ge(100) − by physical vapor deposition (PVD), while another set of Schottky junctions were prepared on the same substrate by depositing either Au or Pt by pulsed laser deposition (PLD).…”

“…The abrupt change in the slope w.r.t such a linear reference marks the appearance of a second onset, which is independently corroborated by looking at the derivative of the intensity.The power law is so close to V 2 that a straight line represents the first derivative well and, the appearance of a second onset determines an easily identifiable abrupt change in the slope of the derivative (behaviour seen around ≈ 0.7 eV in the insets inFigure 5, red lines). In addition,Figure 6shows normal-like probability distributions and Φ i histograms obtained by applying to a set of individual normalized BEES I(V) curves a Levenberg-Marquardt algorithm and Bell-Kaiser's model,29 αV µ , which corresponds to the ab-initio phase-space equation33 for T = 0 K and µ = 2 (an approximation that considerably simplifies…”