Mapping of AlxGa1−xAs band edges by ballistic electron emission spectroscopy

Cheng, X.-C.; Collins, D. A.; McGill, T. C.

doi:10.1116/1.580609

Cited by 10 publications

(4 citation statements)

References 17 publications

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“…The BEEM spectrum for the reference GaAs region had two fitted thresholds at 0:900 eV and 1:200 eV (not shown), corresponding to ÿ and L points of the GaAs conduction band, in good accordance with previous results [14]. The spectrum for the Al 0:3 Ga 0:7 As barrier layers also had two thresholds at 1:085 and 1:210 eV, respectively, which is 60 meV lower than other reports for a similar Al fraction [15,16]. We point out that different surface treatments can result in different SBH values [15], and previous studies used a …”

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confidence: 90%

Direct Measurement of Quantum Confinement Effects at Metal to Quantum-Well Nanocontacts

et al. 2005

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Model metal-semiconductor nanostructure Schottky nanocontacts were made on cleaved heterostructures containing GaAs quantum wells (QWs) of varying width and were locally probed by ballistic electron emission microscopy. The local Schottky barrier was found to increase by 0:140 eV as the QW width was systematically decreased from 15 to 1 nm, due mostly to a large (0:200 eV) quantumconfinement increase to the QW conduction band. The measured barrier increase over the full 1 to 15 nm QW range was quantitatively explained when local ''interface pinning'' and image force lowering effects are also considered. DOI: 10.1103/PhysRevLett.94.206803 PACS numbers: 73.21.Fg, 73.30.+y, 73.63.Hs, 73.63.Rt Much recent activity has focused on nanoscale semiconducting devices [1][2][3][4][5]. Critical to their behavior are the contacts that transport carriers in and out of the device. For example, some argue that the device behavior of carbon nanotube field-effect transistors is dominated by Schottky barriers (SBs) that form at the metal contacts to the nanotube [4,5]. In nm-dimension Schottky contacts, small-size effects-such as quantum confinement and geometryinduced electric fields-may greatly alter carrier transport through the contacts. There is a critical need to predict how these effects scale with contact size and geometry. Several previous studies have measured current-voltage curves through nm-sized metal contacts on homogenous semiconductor (SC) substrates, to infer effects from nonlocal ''environmental pinning'' and geometry-induced electric fields [6,7]. However, those contacts were not to semiconducting nanostructures, so effects such as quantum confinement were negligible. Furthermore, the small-size effects on the Schottky barrier were inferred from current-voltage measurements, and not directly measured with a spectroscopic technique.Here we report nm-resolution measurements of carrier transport through a model metal-SC nanostructure system, in which the nanostructure dimension can be systematically varied down to 1 nm. This model system is made on the cleaved edge of a GaAs wafer containing a series of AlGaAs=GaAs=AlGaAs quantum wells (QWs) of different thickness. The measured quantity is the energy offset between the metal Fermi energy and the SC conduction band minimum: the Schottky barrier height (SBH). The measurement tool is ballistic electron emission microscopy (BEEM) [8,9], which directly measures the local SBH with nanoscale spatial resolution and <20 meV energy resolution. The SBH shows a strong 140 meV systematic increase as the QW width d is reduced to 1 nm. Our measurements agree very well with the predicted increase from simple one-dimensional quantum confinement, adjusted by a smaller calculated decrease (70 meV for a 1 nm QW) due to environmental pinning effects [6,7] and increased image force lowering [10].The samples consisted of a sequence of GaAs QWs (5 10 16 =cm 3 n-type) with width varying between 1 and 15 nm, separated by 200 nm thick Al 0:3 Ga 0:7 As barrier layers (1 10 17 =cm 3 n-typ...

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confidence: 90%

Direct Measurement of Quantum Confinement Effects at Metal to Quantum-Well Nanocontacts

et al. 2005

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“…Initially, BEEM has been used to conduct Schottky barrier and band structure characterization in various material systems, including technologically important semiconductors such as Ga(Al)As [67][68][69], Ga(In)P [70][71][72], Ga(As)N [73][74][75], Si [76,77] and SiC [78].…”

Section: Stm-based Hot Electron Microscopy/spectroscopy Of Heterostru...mentioning

confidence: 99%

Hot electron spectroscopy and microscopy

2004

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Semiconductor heterostructures, such as double-barrier resonant tunnelling diodes and superlattices, are nowadays used for many applications. One very versatile and powerful method to study electronic transport in heterostructures is hot electron spectroscopy. Hot electron spectroscopy can be carried out in two complementary versions: device-based techniques usually employ so-called hot electron transistors (HETs), while ballistic electron emission microscopy (BEEM) uses a scanning tunnelling microscope (STM) as the source of ballistic electrons.In this review, spectroscopic results obtained by these two methods are compared and discussed. It is shown that BEEM results are strongly influenced by electron refraction effects, while the behaviour of HET devices is dominated by inelastic scattering effects in the base and drift region of the device. Thus, STM-based BEEM/S and HET-based spectroscopy are genuinely complementary methods, which yield supplementary results.

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“…Energy and parallel momentum conservation have the effect that the BEEM current, at a given tunnelling bias, is not only sensitive to lateral variations of the potential barriers, but also to any scattering processes taking place between the point of injection at the surface and the collector. BEEM is a very useful technique to investigate the transport-related properties such as Schottky barier height [4,5], MOS structure [6][7][8], band offsets [9,10] and local barrier height between QDs and substrate [11].…”

Section: Introductionmentioning

confidence: 99%

The Ballistic Electron Emission Microscopy in the Characterization of Quantum Dots

Hutagalung

Yaacob

Keat

2007

SSP

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Ballistic electron emission microscopy (BEEM) is a new method by apply the spatial resolution capabilities of the scanning tunneling microscope (STM) to investigate electron transport properties in the quantum dots. This method requires three terminals: a sharp tip to inject electrons, a conductive layer and a semiconductor substrate. The transport-related properties of the sample can be obtained by using the characteristic of the injected and collected electrons. In this paper proposed a BEEM model for the silicon quantum dots (Si-QDs) on SiO2 layer prepared by LPCVD technique. SiO2 layer was thermally grown on p-type Si (100) wafer in dry O2 atmosphere and a thin gold layer cap used to provide a conductive layer on top of the Si-QDs for the BEEM characterization.

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Mapping of AlxGa1−xAs band edges by ballistic electron emission spectroscopy

Cited by 10 publications

References 17 publications

Direct Measurement of Quantum Confinement Effects at Metal to Quantum-Well Nanocontacts

Direct Measurement of Quantum Confinement Effects at Metal to Quantum-Well Nanocontacts

Hot electron spectroscopy and microscopy

The Ballistic Electron Emission Microscopy in the Characterization of Quantum Dots

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