Electronic structure and electron dynamics at Si(100)

Weinelt, Martin; Kutschera, Michael; Schmidt, Ralf; Orth, C. J.; Fauster, Thomas; Rohlfing, Michael

doi:10.1007/s00339-004-3127-7

Cited by 68 publications

(54 citation statements)

References 63 publications

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“…In the case of Si, the surface reconstruction changes from (2×1) to (4×2) below ~ 150 K [83]; while we might not expect this to significantly affect the formation of Ps it should be checked, especially since the electronic surface exciton observed by Wienelt et al [36] was only observed for the (4×2) surface [84]. If there is a thermal contribution to the energy spread of emitted Ps then photoemission from a cold target would provide a narrow beam.…”

Section: Discussionmentioning

confidence: 91%

Positronium formation via excitonlike states on Si and Ge surfaces

et al. 2011

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Recent experiments combining lifetime and laser spectroscopy of positronium (Ps) show that these atoms are emitted from p-Si(100) at a rate that depends on the sample temperature, suggesting a thermal activation process, but with an energy that does not, precluding direct thermal activation as the emission mechanism. Moreover, the amount of Ps emitted is substantially increased if the target is irradiated with 532 nm laser light just prior to the implantation of the positrons. Our interpretation of these data was that the Ps was emitted via an exciton-like positron-electron surface state, not dissimilar to an electronic surface exciton observed on Si in two-photon photoemission measurements. The hypothesis that this state may be populated by electrons from one of the occupied electronic surface states, either thermally or by laser excitation, is consistent with our observations and suggests that one should expect a high Ps yield at room temperature from an n-doped Si(100) sample, since in this case the same surface states will already be occupied. Here we present data obtained with an n-Si(100) target that supports our model, and also reveals the unexpected result that the kinetic energy of Ps emitted from this material actually decreases when it is heated, an effect we attribute to shifts in the surface energy levels due to the presence of a high density of thermally generated electrons. We show data obtained with a Ge(100) sample that corroborate the idea that the effects we observe are related to surface electron states, and hence should occur for any indirect band gap semiconductor with dangling bond states. Our model is further confirmed by the observation that the Ps yield from p-Si depends linearly on the surface density of the implanted positrons due to the effects of electron-hole pairs created as the positrons slow down.

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Section: Discussionmentioning

confidence: 91%

Positronium formation via excitonlike states on Si and Ge surfaces

et al. 2011

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“…With increasing reverse bias, a decrease in the activation energy barrier is expected and so more states, as well as surface states [16], would be generated at the semiconductor interface or insulator interface and more electrons should recombine. More accurately, these should occur at the critical barrier height of < 60meV seen in Figure 7.…”

Section: Figure 6 Dark Current Density As Function Of Inverse Tempermentioning

confidence: 99%

“…The value of carrier concentration (n s ) is strongly dependent on the operation bias voltages at constant temperature, and leads to the exponential behavior of E act, which results in the analytical expression n s ~ exp(-E act /k B T) where n s is the charge carrier concentrations [15,16]. By assuming, n s are proportional to the leakage current I lc with a proportionality factor of I c .…”

Section: Figure 6 Dark Current Density As Function Of Inverse Tempermentioning

confidence: 99%

Low-frequency noise behavior at reverse bias region in InAs/GaSb superlattice photodiodes on mid-wave infrared

et al. 2013

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We describe a relationship between the noise characterization and activation energy of InAs/GaSb superlattice MidWavelength-Infrared photodiodes for different passivation materials applied to the device. The noise measurements exhibited a frequency dependent plateau (i.e. 1/f-noise characteristic) for unpassivated as well as Si 3 N 4 passivated samples whereas 1/f-type low noise suppression (i.e. frequency independent plateau) with a noise current reduction of more than one order of magnitude was observed for SiO 2 passivation. For reverse bias values below -0.15V, the classical Schottky-noise calculation alone did not appear to describe the noise mechanism in a SL noise behavior, which shows a divergence between theoretically and experimentally determined noise values. We identify that, the additional noise appears, with and without passivation, at the surface activation energy of < 60 meV and is inversely proportional to the reverse bias. This is believed to be caused by the surface dangling-bonds (as well as surface states) whose response is controlled by the applied reverse bias. The calculated noise characteristics showed a good agreement with the experimental data.

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“…Electrons bound by the image potential (IPS) were first observed at the surface of liquid helium in 1973 Grimes and Brown 5 . Since then, they have been experimentally investigated on many different surfaces including the noble metals 6,7 , transition metals 2,[8][9][10] , silicon 11 , graphene 12 , and carbon nanotubes 13 . For metallic systems with a surface band gap between the Fermi level and the vacuum level, image potential creates a Rydberg series of bound electronic states.…”

Section: Image Potential Statesmentioning

confidence: 99%

Watching Electrons Transfer from Metals to Insulators using Two Photon Photoemission

Johns

2010

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Ultrafast angle-resolved two photon photoemission was used to study the dynamics and interfacial band structure of ultrathin films adsorbed onto Ag(111). Studies focused on the image potential state (IPS) in each system as a probe for measuring changes in electronic behavior in differing environments.The energetics and dynamics of the IPS at the toluene/Ag(111) interface are strongly dependent upon coverage. For a single monolayer, the first IPS is bound by 0.81 eV below the vacuum level and has a lifetime of 50 femtoseconds (fs). Further adsorption of toluene creates islands of toluene with an exposed wetting layer underneath. The IPS is then split into two peaks, one corresponding to the islands and one corresponding to the monolayer. The wetting layer IPS shows the same dynamics as the monolayer, while the lifetime of the islands increases exponentially with increasing thickness. Furthermore, the island IPS transitions from delocalized to localized within 500 fs, and electrons with larger parallel momenta decay much faster. Attempts were made using a stochastic model to extract the rates of localization and intraband cooling at differing momenta.In sexithiophene (6T) and dihexyl-sexithiophene (DH6T), the IPS was used as a probe to see if the nuclear motion of spectating side chains can interfere with molecular conduction. The energy and band mass of the IPS was measured for 6T and two geometries of DH6T on Ag(111). Electrons injected into the thicker coverages of DH6T grew exponentially heavier until they were completely localized by 230 fs, while those injected into 6T remained nearly free electron like. Based off of lifetime arguments and the density of defects, the most likely cause for the mass enhancement of the IPS in this system is small polaron formation caused by coupling of the electron to vibrations of the alkyl substituents. The energetic relaxation of the molecular adsorbate was also measured to be 20 meV/100 fs for the DH6T, and 0 meV/100 fs for the 6T. This relaxation is consistent with the localization of the charge creating a barrier for it moving from one lattice site to a neighboring one.Finally, the IPS was used to study the evolution of the surface band gap at the Mg/Ag(111) interface. The Mg(0001) surface band gap lies 1.6 eV below the Fermi level, and consequently shows no peak in the projected density of states for the IPS. A method for creating layer by layer growth of Mg on Ag(111) was determined using Auger Spectroscopy and low energy electron diffraction. By monitoring the decay of the 1 2 intensity of the IPS versus coverage, it was determined that four layers of magnesium on Ag(111) is sufficient to completely eliminate the surface band gap

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Electronic structure and electron dynamics at Si(100)

Cited by 68 publications

References 63 publications

Positronium formation via excitonlike states on Si and Ge surfaces

Positronium formation via excitonlike states on Si and Ge surfaces

Low-frequency noise behavior at reverse bias region in InAs/GaSb superlattice photodiodes on mid-wave infrared

Watching Electrons Transfer from Metals to Insulators using Two Photon Photoemission

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