First direct observation of EL2-like defect levels in annealed LT-GaAS |
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| Authors: | N D Jäger A K Verma P Dreszer N Newman Z Liliental-Weber M van Schilfgaarde E R Weber |
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| Affiliation: | (1) Department of Materials Science, University of California, 94720 Berkeley, CA;(2) Lawrence Berkeley Laboratory, Materials Science Division, 94720 Berkeley, CA;(3) Department of Electrical Engineering, University of California, 94720 Berkeley, CA;(4) Stanford Research International, 94025 Menlo Park, CA;(5) Present address: Physics Dept. E-16, Technical University, München, Germany |
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| Abstract: | Nonstoichiometric arsenic-rich GaAs grown at low temperatures by molecular beam epitaxy (LT-GaAs) has been found to be semi-insulating
after high-temperature annealing. The origin of this technologically important conversion is not yet fully understood. In
order to study this effect, we performed photocurrent measurements on p-LT GaAs-n diodes in the spectral range between 0.75
and 1.5eV at 8K. The photocurrent spectra revealed the following features which are unique to the EL2 level: photoquenching,
characteristic photoionization transitions to conduction band minima and a presence of a broad band due to the effect of auto-ionization
from the excited state. Moreover, modeling of the optical excitation process using realistic band structure demonstrates that
these features cannot be explained by “internal photoemission” originating from As precipitates, as the “buried Schottky barrier
model” predicts. This is the first direct experimental evidence for the existence of EL2-like defect levels and their importance
for understanding the optical and electronic properties of annealed LT-GaAs. |
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| Keywords: | Defect EL2 defect internal photoemission low-temperature grown GaAs photocurrent photoquenching |
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