Band-gap measurements of direct and indirect semiconductors using monochromated electrons

Journal Article · Tue May 15 00:00:00 EDT 2007 · Physical Review. B, Condensed Matter and Materials Physics

DOI:https://doi.org/10.1103/PHYSREVB.75.195214· OSTI ID:20951430

Lin, Gu; Srot, Vesna; Sigle, Wilfried; Koch, Christoph; Aken, Peter van; Ruehle, Manfred ^[1]; Scholz, Ferdinand; Thapa, Sarad B; Kirchner, Christoph ^[2]; Jetter, Michael ^[3]

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1. Max-Planck Institute for Metals Research, Heisenbergstrasse 3, D-70569 Stuttgart (Germany)
2. Institute of Optoelectronics, University of Ulm, Albert-Einstein-Allee 45, D-89069 Ulm (Germany)
3. Institut fuer Strahlenphysik, University of Stuttgart, D-70569 Stuttgart (Germany)

With the development of monochromators for transmission electron microscopes, valence electron-energy-loss spectroscopy (VEELS) has become a powerful technique to study the band structure of materials with high spatial resolution. However, artifacts such as Cerenkov radiation pose a limit for interpretation of the low-loss spectra. In order to reveal the exact band-gap onset using the VEELS method, semiconductors with direct and indirect band-gap transitions have to be treated differently. For direct semiconductors, spectra acquired at thin regions can efficiently minimize the Cerenkov effects. Examples of hexagonal GaN (h-GaN) spectra acquired at different thickness showed that a correct band-gap onset value can be obtained for sample thicknesses up to 0.5 t/{lambda}. In addition, {omega}-q maps acquired at different specimen thicknesses confirm the thickness dependency of Cerenkov losses. For indirect semiconductors, the correct band-gap onset can be obtained in the dark-field mode when the required momentum transfer for indirect transition is satisfied. Dark-field VEEL spectroscopy using a star-shaped entrance aperture provides a way of removing Cerenkov effects in diffraction mode. Examples of Si spectra acquired by displacing the objective aperture revealed the exact indirect transition gap E{sub g} of 1.1 eV.

• OSTI ID: 20951430
• Journal Information: Physical Review. B, Condensed Matter and Materials Physics, Vol. 75, Issue 19; Other Information: DOI: 10.1103/PhysRevB.75.195214; (c) 2007 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA); ISSN 1098-0121
• Country of Publication: United States
• Language: English

Related Subjects

75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
62 RADIOLOGY AND NUCLEAR MEDICINE
CHERENKOV RADIATION
DIFFRACTION
ELECTRONS
ENERGY GAP
ENERGY-LOSS SPECTROSCOPY
EV RANGE 01-10
GALLIUM NITRIDES
MOMENTUM TRANSFER
OMEGA BARYONS
SEMICONDUCTOR MATERIALS
SILICON
SPATIAL RESOLUTION
SPECTRA
THICKNESS
TRANSMISSION ELECTRON MICROSCOPY