Comparisons using optoelectronic modulation spectroscopy of n-type GaAs epitaxial layers formed on buffer layers prepared at normal and low temperatures |
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Authors: | Chi-Hsin Chiu J G Swanson |
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Affiliation: | (1) Department of Electronic Engineering, King’s College London, WC2R 2LS, United Kingdom |
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Abstract: | Optoelectronic modulation spectroscopy (OEMS) has been used to examine defect-related states in GaAs metal-semiconductor,
field-effect transistor (MESFET) structures prepared by molecular-beam epitaxy (MBE) on buffer layers formed at normal and
low temperatures. The technique was used to simultaneously observe the spectra of defect states near to the interface with
the buffer layer and in the active layer. There were few responses that were common to the structures. The most prominent
was an electron trap with a depth of 0.92 eV. This was present throughout both structures and may be from a native defect
in GaAs. With few exceptions the states seen in a particular structure were present in the active layer as well as near to
the interface with the buffer layer suggesting that, in each case, the defects originated from the active/buffer layer interface
or from the buffer layer. The most significant difference was that states in the low-temperature (LT)-based structure generally
exhibited replicating responses with specific energy periodicities. A model describes this in terms of optical-absorption
transitions to the local vibrational states of defects. Five different replica series were observed. The vibrational characteristics
of the defects found in the LT material suggest that they are different in character and extent to those defects found in
material formed on a normally prepared buffer layer. Their Frank-Condon energies ranged from 9–332 meV. |
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Keywords: | Optical absorption defect electron states GaAs LT GaAs vibrational states buffer layers |
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