Ballistic Electron Emission Microscopy Images Research Articles

Hot carrier scattering at interfacial dislocations observed by ballistic-electron-emission microscopy.

In situ ballistic-electron-emission microscopy (BEEM) has been performed at 77 K on partially strain-relaxed, epitaxial Co${\mathrm{Si}}_{2}$/Si(111) films grown by molecular beam epitaxy. Hot electron scattering at individual interfacial dislocations has been observed for the first time by BEEM. Standing wave formation in the metal and changes of the surface electronic structure give rise to significant contrast in BEEM images. Apart from the dislocation- and surface-induced contrast, the interfacial transmission is generally found to be homogeneous.

Dynamical transmission effects and impact ionization in hot-electron transport across NiSi2/Si(111)7×7 interfaces

Impact ionization and interface transmission, two important processes in hot-electron transport in semiconductor structures, have been studied by ballistic electron emission microscopy (BEEM) at interfaces of NiSi2/n-Si(111)7×7. The analysis of BEEM spectra taken in pinholes of thin NiSi2 films allows a direct determination of the quantum yield of impact ionization in Si over a wide energy range (≳7 eV). BEEM images and spectra recorded on NiSi2 terraces show evidence for the conservation of transverse momentum and a small probability for normal interface transmission up to high energies (≊4 eV above the Fermi energy), in accordance with dynamical calculations of the transmission probabilities.

Ballistic electron emission microscopy of the Au-Si (100) interface

In this paper, experiments performed on Au-Si (100) junctions by Ballistic Electron Emission Microscopy (BEEM), a method for studying the metal-semiconductor interface, are presented. BEEM spectra show a characteristic threshold that yields the Schottky barrier height at the interface. The average barrier height is found to be lower than the usual values of Au-Si contacts. BEEM images result from the spatial variations of the current in the semiconductor and present unusual local contrasts. These phenomena are analysed in terms of interface quality

Hot-carrier scattering in a metal: A ballistic-electron-emission microscopy investigation on PtSi

Ballistic-electron-emission microscopy (BEEM) has been used to study the PtSi/n-type Si(100) interface. Hot-electron transport has been investigated by measuring the ballistic-electron transmission as a function of position (BEEM imaging), energy (BEEM spectroscopy), and PtSi thickness (BEEM attenuation length). Hot-hole transport and electron-electron scattering have also been investigated as a function of these parameters. This study has been conducted on in situ fabricated PtSi/n-type Si(100) Schottky diodes in UHV with the silicide thickness ranging from 20 to 500 \AA{}. The PtSi films were granular and the BEEM transmissivity was found to be homogeneous on individual grains but strongly varying from one grain to another. We attempt to compare the absolute BEEM current level with existing models and find its limiting value for small silicide thicknesses to be close to 1 depending on the model considered, indicating efficient transmission due to strong forward focusing of the electrons in the base or enhancement due to multiple scattering within the grains. BEEM current as a function of silicide thickness shows a change from a rapid to a slower decrease at about 150 \AA{}. Reverse BEEM (RBEEM) attenuation lengths also show this qualitative behavior, but the attenuation with increasing PtSi thickness is distinctly weaker, indicating that BEEM and RBEEM intensities are differently influenced by the elastic and inelastic hot-carrier mean free paths. RBEEM spectra are found to be anomalous, indicating an anomalous distribution of the tunnel-injected hot holes in the base.

Density of states and hot electron effects in ballistic electron emission spectroscopy

Ballistic electron emission microscopy (BEEM) and BEEM spectroscopy are reported for thin (≊50 Å) Cr layers on n-type GaP(110). BEEM images reveal that current transport across the interface occurs primarily in the vicinity of grain boundaries where the Cr is thinnest, and on small (<200 Å in diameter) surface patches that are relatively smooth and parallel to the interface. For the conventional electron injection mode, the collector current Ic exhibits pronounced but broad structures near tip biases VT of 4 and 6 V, whose origin is attributed to density of states effects in the semiconductor. For VT≳7 V, Ic was frequently observed to exceed the (constant) scanning tunneling microscope tip current. Under reverse bias (electron extraction) a novel hole current was observed for VT≳1.7 V, which, following an initial rise with increasing bias, would saturate and then decay, often leading to a polarity reversal for VT≳5.5 V. This behavior, as well as the large Ic observed at high forward bias, is attributed to impact ionization in the depletion region of the semiconductor. In addition to the conventional threshold in Ic at 1.31 V, attributed to electron transmission across the Schottky barrier into the X1 conduction band minima, a second, more pronounced threshold at 1.69 V was observed for the first time for GaP. It is assigned to electron transfer into the higher lying L1 and X3 conduction band minima.

Ballistic-electron-emission microscopy and spectroscopy of GaP(110)-metal interfaces.

Ballistic-electron-emission-microscopy (BEEM) studies of Mg, Ni, Cu, Ag, and Au films on cleaved n-type GaP (110) show uniform Schottky-barrier heights across the surfaces, which varied from 1.02 eV for Mg to 1.41 eV for Au. BEEM images reveal areas of sharp current variations (contrast) that coincide with topographic gradients on the metal surfaces. Deduced Schottky-barrier heights depend on the transport model; a 5/2 power-law dependence of the BEEM current on applied voltage results if nonclassical transmission across the interface is included