Photoemissive Determination of Barrier Shape in Tunnel Junctions

Braunstein, A.; Braunstein, M.; Picus, G. S.; Mead, C. A.

doi:10.1103/physrevlett.14.219

Cited by 87 publications

(20 citation statements)

References 5 publications

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“…These measurements also eliminate some earlier suggested models for the magnetoelectric effect, but remain consistent with the symmetry requirements for the observation of a magnetoelectric effect in this material. Our results firmly establish the model used by Bertaut et al 3 to interpret their unpublished zero-field neutron diffraction measurements with powders.…”

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confidence: 84%

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Hot-Electron Attenuation in ThinAl2O3Films

Braunstein

Picus

1965

Phys. Rev. Lett.

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A number of recent reports have shown that much information concerning the barrier heights in tunnel barrier structures of the type AlAl 2 O s -Al can be obtained from internal photoemission experiments. 1 " 5 The observed photocurrents in these structures are interpreted as being due to hot electrons, generated in the aluminum electrodes, which are energetic enough to overcome the 1.5-to 2-eV interfacial barriers and thus enter the A1 2 0 3 conduction band-the net current is then the difference of the currents from the two electrodes. In order to understand the results under all conditions of applied voltage and incident photon energy it has been necessary to make two assumptionSo First, there are unequal densities of hot electrons reaching the two Al-Al 2 O s interfaces due to the optical-absorption process and the hot-electron transport in the electrodes. Second, the current due to electrons which are traversing the A1 2 0 3 conduction band in the direction opposite to the net field in the Al 2 O s (the sum of the applied field and the internal field that is always present 6 ) is attenuated due to scattering or other energy-or momentumloss processes. Electrons which are traveling with the field will reach the opposite electrode in spite of any such processes, while those opposed to it will have a high probability of being returned to the electrode in which they originated oMost of the reported measurements have been taken with the light incident on the upper or counter electrode of the structure, which is the one with the higher interfacial barrier height. In two cases, however, experiments were also done with the light incident on the electrode which was deposited on the glass substrate, and it was discovered that the photocurrent changed sign. 1 ' 5 It is the purpose of this Letter to show the spectral dependence of the photocurrent with this direction of illumination and to show that it can be used to give quantitative verification of the two assumptions made above.Experimental samples were prepared as previously described, 3 with the exception that the electrodes were both semitransparent and of equal thickness. The Al 2 O s thickness was approximately 40 A. The measurements were taken with an optical system which had two beams of equal intensity which illuminated the two electrodes. Shutters could be placed in either beam so that photoemission could be measured with the electrodes separately illuminated or with both illuminated simultaneously. Figure 1 shows the photoresponses obtained as a function of photon energy with zero applied bias voltage when the electrodes are separately illuminated. The R 21 current is the one which has usually been observed. When the square root of R 21 is plotted against photon energy, the result is linear with an extrapolated photothreshold of 1.96 eV, which is interpreted as the Al-Al 2 O s barrier height for the top electrode of the structure (generally denoted by

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confidence: 84%

“…Experimental samples were prepared as previously described, 3 with the exception that the electrodes were both semitransparent and of equal thickness. The Al 2 O s thickness was approximately 40 A.…”

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confidence: 99%

Hot-Electron Attenuation in ThinAl2O3Films

Braunstein

Picus

1965

Phys. Rev. Lett.

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“…1(a)] due to the conservation of the electric displacement (Gauss' law). This effect was theoretically proposed more than forty years ago 11 based on the early studies of metal/dielectric interfaces [12][13][14][15][16] , and it was suggested that it should be dominant over image force or tunneling contributions in the limit of large S ε . Practically, however, this effect is negligible in conventional semiconductors, and the assumption of perfect screening in the abrupt junction approximation provides a quantitatively accurate band diagram.…”

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confidence: 99%

Electric field penetration in Au/Nb:SrTiO3 Schottky junctions probed by bias-dependent internal photoemission

Hikita

Kawamura

Bell

et al. 2011

Applied Physics Letters

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Electric field penetration into the metallic side of a Schottky junction is in principle a universal phenomenon, the magnitude of which increases with the semiconductor permittivity. Here, we quantitatively probe this effect using bias-dependent internal photoemission spectroscopy at the Schottky junction between a large dielectric permittivity semiconductor SrTiO 3 and gold. A clear linear reduction of the barrier height with increasing interface electric field was observed, highlighting the importance of field penetration into the gold. The interfacial permittivity of SrTiO 3 at the interface is reduced from the bulk value, reflecting intrinsic suppression at the interface. a)

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“…This difference is conjectured to be due to inelastic scattering in the built-in field in the oxide conduction band. 8 The current due to electrons excited in the bottom electrode and traversing the oxide layer opposite to the built-in field will be attenuated. In contrast, electrons excited in the top electrode will reach the opposite electrode in spite of such processes.…”

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Oxidation process of AlOx-based magnetic tunnel junctions studied by photoconductance

Vanhelmont

Boeve

Coehoorn

et al. 2003

Journal of Applied Physics

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The oxidation process of Co/AlOx/Co magnetic tunnel junctions has been investigated by photoconductance, in addition to traditional transport measurements. The shape of the photoconductance curves is explained within the framework of a simple qualitative model, assuming an oxidation time dependent imbalance of the incident forward and reverse hot electron fluxes, as well as inelastic scattering processes in the oxide. Due to the large sensitivity of the technique, the presence of unoxidized Al beneath the barrier layer can be monitored very accurately. The disappearance of a negative contribution to the photocurrent indicates the complete oxidation of the barrier layer, which coincides with the maximum magnetoresistance. From a Fowler analysis, the barrier height is determined as a function of oxidation time. The observed disagreement of the effective barrier heights determined by this technique and those found by Simmons fits demonstrates the added value of photoconductance studies.

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Photoemissive Determination of Barrier Shape in Tunnel Junctions

Cited by 87 publications

References 5 publications

Hot-Electron Attenuation in ThinAl2O3Films

Hot-Electron Attenuation in ThinAl2O3Films

Electric field penetration in Au/Nb:SrTiO3 Schottky junctions probed by bias-dependent internal photoemission

Oxidation process of AlOx-based magnetic tunnel junctions studied by photoconductance

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