Optical Absorption of point defects in AlN crystals as measured by photo-induced electron paramagnetic resonance
ORAL · Invited
Abstract
AlN is actively pursued as a substrate for high power electronics due to its large bandgap (~ 6 eV) and high critical field (15 MV/cm). The ultrawide bandgap also enables production of emitters and detectors that are operational in the ultraviolet. We have performed 10 GHz room temperature electron paramagnetic resonance (EPR) measurements in combination with illumination to study a prominent point defect in AlN. The photo-induced EPR technique offers an advantage over conventional absorption measurements because the defect itself is monitored, rather than the material as a whole.
An extensive series of measurements by others indicates that the main EPR signal studied here is due to an axial Al centered on a nitrogen site [1]. The spectrum has been assigned to a nitrogen vacancy (VN0) or substitutional oxygen (ON0). However, recognizing that the resonance may be caused by the presence of any impurity with nearly 0 nuclear spin, our optically induced EPR studies suggest a third alternative. By illuminating the sample at room temperature, we show that the EPR signal is activated at 3.8 eV and subsequently quenched at about 1.8 eV. Neither threshold is consistent with an assignment as a ON since oxygen is expected to be a shallow donor in AlN. While the 3.8 eV absorption threshold is reasonably close to that expected for VN, comparison with optical transitions reported in the literature, suggests that carbon substituting for nitrogen, CN0, agrees more closely with the optical and EPR data. Thus, by combining EPR directly with illumination, we suggest a reassignment of the EPR signal and support identification of the ~ 4 eV absorption threshold and predicted defect level. The talk will highlight the role of carbon in AlN and the potential limitations facing both optical and electronic applications.
[1] V.A. Soltamov et al, J. Appl. Phys. 107, 113515 (2010).
This work was supported as part of the Ultra Materials for a Resilient Energy Grid, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award # DE-SC0021230.
An extensive series of measurements by others indicates that the main EPR signal studied here is due to an axial Al centered on a nitrogen site [1]. The spectrum has been assigned to a nitrogen vacancy (VN0) or substitutional oxygen (ON0). However, recognizing that the resonance may be caused by the presence of any impurity with nearly 0 nuclear spin, our optically induced EPR studies suggest a third alternative. By illuminating the sample at room temperature, we show that the EPR signal is activated at 3.8 eV and subsequently quenched at about 1.8 eV. Neither threshold is consistent with an assignment as a ON since oxygen is expected to be a shallow donor in AlN. While the 3.8 eV absorption threshold is reasonably close to that expected for VN, comparison with optical transitions reported in the literature, suggests that carbon substituting for nitrogen, CN0, agrees more closely with the optical and EPR data. Thus, by combining EPR directly with illumination, we suggest a reassignment of the EPR signal and support identification of the ~ 4 eV absorption threshold and predicted defect level. The talk will highlight the role of carbon in AlN and the potential limitations facing both optical and electronic applications.
[1] V.A. Soltamov et al, J. Appl. Phys. 107, 113515 (2010).
This work was supported as part of the Ultra Materials for a Resilient Energy Grid, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award # DE-SC0021230.
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Presenters
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Mary Ellen Zvanut
University of Alabama at Birmingham
Authors
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Mary Ellen Zvanut
University of Alabama at Birmingham