Compensating defects and mechanisms in AlN and AlGaN
ORAL · Invited
Abstract
AlN, with a 6 eV ultrawide bandgap and critical field as high as 15 MV/cm, is considered a viable material for high power electronics and deep UV devices. However, electrical compensation is limiting advances in device development. We have performed 10 GHz electron paramagnetic resonance (EPR) measurements in combination with illumination and thermal annealing to investigate the compensation mechanisms in AlN bulk crystals and AlGaN films. The bulk crystals contain a background concentration of C, Si, and O on the order of 1019 cm-3 for one set and 1017 cm-3 for the other set. The AlGaN films were intentionally doped with either Si or Ge to ~1019 cm-3, with background impurities below 1017 cm-3.
The bulk crystals are dominated by two different defects. One was recently identified as CN0[1]. Photo-EPR measurements of CN0, in combination with first principles calculations, show that the carbon has a neutral to negative charge transition level about 2 eV above the valence band edge, confirming its role as a compensating center in AlN. The second center observed in several of the crystals and Si-doped films is the neutral donor. The EPR signal must be generated with >1.3 eV light, and the resulting signal is metastable. Detailed experiments which explore this metastability show that the temperature at which the neutral donor quenches increases as x decreases in AlxGa1-x N, independent of the dopant atom, Si or Ge. Such behavior is surprising if one views the thermal quenching as removal of an electron from the donor to the conduction band, but is reasonable in the ‘DX picture’ where the excited electron is captured by another neutral donor and forms the stable negative charge state. The talk will address the robustness of this model in films with varied Si concentration and Al mole fraction. Combined with information about the carbon acceptor, the work addresses the complex dynamics of compensation in AlN.
The bulk crystals are dominated by two different defects. One was recently identified as CN0[1]. Photo-EPR measurements of CN0, in combination with first principles calculations, show that the carbon has a neutral to negative charge transition level about 2 eV above the valence band edge, confirming its role as a compensating center in AlN. The second center observed in several of the crystals and Si-doped films is the neutral donor. The EPR signal must be generated with >1.3 eV light, and the resulting signal is metastable. Detailed experiments which explore this metastability show that the temperature at which the neutral donor quenches increases as x decreases in AlxGa1-x N, independent of the dopant atom, Si or Ge. Such behavior is surprising if one views the thermal quenching as removal of an electron from the donor to the conduction band, but is reasonable in the ‘DX picture’ where the excited electron is captured by another neutral donor and forms the stable negative charge state. The talk will address the robustness of this model in films with varied Si concentration and Al mole fraction. Combined with information about the carbon acceptor, the work addresses the complex dynamics of compensation in AlN.
- D. Wickramaratne et al, Phys. Rev. Materials 8, 094602 (2024).
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Publication: D. Wickramaratne et al, Phys. Rev. Materials 8, 094602 (2024).
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
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Shafiqul I Mollik
UNIVERSITY OF ALABAMA AT BIRMINGHAM
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Jason I Forbus
University of Alabama at Birmingham, UNIVERSITY OF ALABAMA AT BIRMINGHAM