Ballistic Electron Emission Microscopy of Semiconductor Interfaces PDF Download

Author: Angela Elizabeth Fowell
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Category :
Languages : en
Pages : 308

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Author: Mario Prietsch
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Category : Interfaces (Physical sciences)
Languages : en
Pages : 69

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Author: Angela D. Davies
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Category :
Languages : en
Pages : 562

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Category :
Languages : en
Pages : 6

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This final report describes an experimental system aimed studying a novel characterization method of metal-semiconductor interfaces which combines ballistic electron emission microscopy (BEEM) with optical excitations. The idea is that the spreading resistance, or space charge, associated with the ballistic electrons injected into the Schottky barrier by the tip of a scanning tunneling microscope (STM), can be modulated by optical excitation. The local photoresponse can therefore be mapped spatially across the barrier, below the metal electrode into which the STM is tunneling. The proposed technology will also enable one to directly measure the lifetime of the photoexcited carriers below the metal electrode, using short laser pulses at different wavelengths. The experimental system has been built, BEEM images acquired, and 1(V) curved measured. Lack of sufficient finding led to the termination of the project.

Author: Cristian Alexandru Tivarus
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Category : Diodes, Schottky-barrier
Languages : en
Pages : 233

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Abstract: A number of possible near and long term semiconductor device technologies rely on abrupt metal-semiconductor interfaces with nm-dimensions, and with internal nm-scale inhomogeneity. It is therefore very important to be able probe the electronic properties of these buried interfaces with sub-10 nm resolution and to find out the impact of small-size effects on their transport properties. In our study we used Ballistic Electron Emission Microscopy (BEEM) and finite-element electrostatic modeling to quantify how small-size effects modify the energy barrier at metal/semiconductor quantum wells (QWs), formed by making Schottky contacts to cleaved edges of GaAs quantum wells. Our model semiconductor heterostructure is formed as a sequence of AlGaAs/GaAs/AlGaAs layers and contains a sequence of GaAs QWs with thickness between 1 and 15 nm. The Schottky barrier height (SBH) measurements as a function of QW thickness showed that the SBH value increases as the QW thickness is decreased, by up to 140 meV for a 1 nm thick QW. This is mostly due to a large quantum-confinement increase (200 meV for a 1nm QW), modified by smaller decreases due to environmental electric field effects. Our modeling gave excellent quantitative agreement with measurements for a wide range of QW thickness when both these effects are considered. In a separate study, the cleaved QW were used as nm-apertures to estimate the resolution of BEEM as a function of metal film thickness. We found that BEEM resolution degrades as the top metal film layer is made thicker, from 12 nm for a 4 nm thick Au layer, up to 22 nm for a 15 nm thick Au layer. Also presented is modeling of the electrostatic potential profile around charged threading dislocations (TD) in GaN, close to a metal-semiconductor interface, and its dependence on the energy of acceptor sites along the dislocation. We found that for energy values higher than 1.13 eV the near interface TD acceptors are completely filled right up to the interface. This results in a very large negative space charge and an increase in the local barrier height close to the TD core that should be observable by techniques such as BEEM.

Author:
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Category :
Languages : en
Pages : 48

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In this final report, we have summarized our work in five areas. The first area, covered in Sec. I, is the development of calcium fluoride tunnel barriers which may be used to increase the operating temperature of PtSi SBIRDs. In particular, we have demonstrated a new technique for growth of exactly two monolayers of CaF2 on Si(l 11) substrates. In Sec. II, we describe our work with ballistic electron emission microscopy to determine electron scattering processing in thin metal layers and at metaliSi interfaces. During this contract, we constructed an in-situ STM/BEEM system which allowed us to make measurements directly on PtSi and Pt surfaces without having to protect these surfaces from oxidation. Our preliminary results with this instrument are described in Sec. III. Sec. IV describes the theoretical model we have developed which explains why the Fowler-like behavior typically observed in the photoresponse for many Schottky-barrier metal/semiconductor interfaces does not prove that crystal momentum parallel to the interface is conserved. In Sec. V, we describe the Monte-Carlo program that we have developed to model ballistic electron scattering in this metal layers and across the metal/semiconductor interface. Initial results demonstrate that electron (or hole) scattering at the metal/semiconductor interface may, in fact, be the dominant transmission mechanism for most (nonpitaxial) metal/semiconductor systems.

Author:
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ISBN:
Category :
Languages : en
Pages : 44

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Partial contents: Electron transport across interfaces and surfaces: an overview; BEEM studies of strain-tuned semiconductor interfaces; Transport studies in semiconductor heterostructures using BEEM; Spectroscopic studies of quantum-wells and -wires using an STM; BEEM in pinholes of NiS2 films on n- Si(111)-7x7: determination of the impact ionization quantum yield in Si; Low- temperature UHV BEEM of epitaxial CoSi2/Si(111); Interfacial barrier studies of epitaxial CoGa on n-type (100) GaAs with BEEM; BEEM on Au/Si(111)7x7 and Au/ CaF2/Si(111)7x7; Temperature dependence of Schottky barriers as probed by BEEM; Nanoscopic barrier height distributions at metal/semiconductor interfaces and observation of critical lengths; BEEM studies of reversed-biased Schottky diodes; Ballistic models applied to low-temperature BEEM measurements of Au/Si interfaces; Electron inelastic mean free path and spatial resolution of BEEM.

Author: Francesca Diane Pardo
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Category : Diodes, Schottky-barrier
Languages : en
Pages : 344

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In this dissertation, three experiments are discussed. The first BEEM (Ballistic Electron Emission Microscopy) characterization of an InAlAs Schottky barrier, an investigation into the possibility of field pinch-off in Au/GaAs samples, and the first demonstration of BEEM on a cleaved multilayer cross-section. Covers results for BEEM research, focusing on BEEM resolution and noise analysis.

Author: Angela Elizabeth Fowell
Publisher:
ISBN:
Category :
Languages : en
Pages :

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Author: Yann Claveau
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Category :
Languages : en
Pages : 0

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After the discovery of Giant Magneto-Resistance (GMR) by Albert Fert and Peter Grünberg, electronics had a breakthrough with the birth of a new branch called spintronics. This discipline, while still young, exploit the spin of electrons, for instance to store digital information. Most quantum devices exploiting this property of electrons consist of alternating magnetic and nonmagnetic thin layers on a semiconductor substrate. One of the best tools used for characterizing these structures, invented in 1988 by Kaiser and Bell, is the so-called Ballistic Electron Emission Microscope (BEEM). Originally, this microscope, derived from the scanning tunneling microscope (STM), was dedicated to the imaging of buried (nanometer-scale) objects and to the study of the potential barrier (Schottky barrier) formed at the interface of a metal and a semiconductor when placed in contact. With the development of spintronics, the BEEM became an essential spectroscopy technique but still fundamentally misunderstood. It was in 1996 that the first realistic model, based on the non-equilibrium Keldysh formalism, was proposed to describe the transport of electrons during BEEM experiments. In particular, this model allowed to explain some experimental results previously misunderstood. However, despite its success, its use was limited to the study of semi-infinite structures through a calculation method called decimation of Green functions. In this context, we have extended this model to the case of thin films and hetero-structures like spin valves: starting from the same postulate that electrons follow the band structure of materials in which they propagate, we have established an iterative formula allowing calculation of the Green functions of the finite system by tight-binding method. This calculation of Green's functions has been encoded in a FORTRAN 90 program, BEEM v3, in order to calculate the BEEM current and the surface density of states. In parallel, we have developed a simpler method which allows to avoid passing through the non-equilibrium Keldysh formalism. Despite its simplicity, we have shown that this intuitive approach gives some physical interpretation qualitatively similar to the non-equilibrium approach. However, for a more detailed study, the use of “non-equilibrium approach” is inevitable, especially for the detection of thickness effects linked to layer interfaces. We hope these both tools should be useful to experimentalists, especially for the Surfaces and Interfaces team of our department.