Donor states in GaAs under hydrostatic pressure

Liu, X.; Samuelson, Lars; Pistol, Mats‐Erik; Gerling, M.; Nilsson, S.

doi:10.1103/physrevb.42.11791

Cited by 23 publications

(19 citation statements)

References 46 publications

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“…The upward-shifted curves correspond to the states of the Τ2 symmetry. Comparing these results with the experimental data [1][2][3][4], we see that the slope of the curve, which corresponds to case (i) is too large. This leads to a suggestion that none of the observed [2,3] group-VI donor states possesses the Α1 symmetry.…”

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confidence: 74%

“…Therefore, we can treat our results as being in agreement with experiment (within the experimental error). This leads to the conclusion that the three possible states of strongly localized donors cannot be excluded from the interpretation of the experimental results [1][2][3][4], i.e., states of A1 and Τ2 symmetry at the cation (Ga) site, and states of Τ2 symmetry at the anion (As) site. Under the hydrostatic pressure, the shift of the center of gravity of the conduction bands mostly affects the donor pressure coefficients.…”

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confidence: 93%

“…The results of experiments [1][2][3][4] for the strongly localized donor states in GaAs under hydrostatic pressure have been interpreted in different manners. Liu et al [1] suggest that all strongly localized donor states possess comparable pressure coefficients (about 1 meV/kbar with respect to the valence-band maximum). Dmochowski et al [2][3][4] argue that the pressure coefficients for the group-IV donors (Si, Ge, Sn) take on the values about 2 meV/kbar, but for the group-VI donors (S, Se) are close to zero.…”

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confidence: 99%

“…Under hydrostatic pressure, the hydrogen-like energy levels change according to the associated conduction-band minimum, whereas the energy levels of the strongly localized states are resonant with the conduction band at the ambient pressure and enter the gap at high pressure. The results of experiments [1][2][3][4] for the strongly localized donor states in GaAs under hydrostatic pressure have been interpreted in different manners. Liu et al [1] suggest that all strongly localized donor states possess comparable pressure coefficients (about 1 meV/kbar with respect to the valence-band maximum).…”

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Anion-Cation Site Dependence of Pressure Coefficients for Donors in GaAs

Bednarek

Adamowski

1995

Acta Phys. Pol. A

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The theoretical model, based on the many-band approach, is proposed for the strongly localized donor states in GaAs. The pressure coefficients for the states of Α1 and Τ2 symmetry have been calculated for the donors at the anioii and cation sites. The obtained results show that these pressure coefficients are different from the conduction-band pressure coefficients and are dependent on the lattice site occupied by the impurity as well as on the symmetry of the donor states.PACS numbers: 71.55.-iIn GaAs, the substitutional donor impurities of groups IV and VI can form weakly localized hydrogen-like states as well as strongly localized states. Both the types of donor states can yield energy levels in the gap. Under hydrostatic pressure, the hydrogen-like energy levels change according to the associated conduction-band minimum, whereas the energy levels of the strongly localized states are resonant with the conduction band at the ambient pressure and enter the gap at high pressure. The results of experiments [1][2][3][4] for the strongly localized donor states in GaAs under hydrostatic pressure have been interpreted in different manners. Liu et al. [1] suggest that all strongly localized donor states possess comparable pressure coefficients (about 1 meV/kbar with respect to the valence-band maximum). Dmochowski et al. [2][3][4] argue that the pressure coefficients for the group-IV donors (Si, Ge, Sn) take on the values about 2 meV/kbar, but for the group-VI donors (S, Se) are close to zero. The assignment of symmetry to these states is also not evident. On the one hand, all these states are interpreted as the states of Α 1 symmetry [2-4], on the other hand, the states of Τ2 symmetry cannot be excluded [5]. For the Ge donor, the anticrossing, observed in Ref. [6] under high hydrostatic pressure, between the energy levels of the hydrogen-like 1s state and the strongly localized donor state permits us to assign the Α 1 symmetry to this state.The pressure dependence of the donor states was the subject of few theoretical papers (e.g. [5,7,8]). However, the applied methods are useful either for hydrogen-like donors [5] or for the impurities with deep energy levels [7,8]. The donor levels in GaAs, although associated with the donor states of strong localization, are close to the conduction-band minimum. Therefore, we are dealing with the shallow energy levels both for the weakly and strongly localized donor (671)

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confidence: 93%

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Anion-Cation Site Dependence of Pressure Coefficients for Donors in GaAs

Bednarek

Adamowski

1995

Acta Phys. Pol. A

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“…Later studies showed that DX centers could be formed in GaAs under hydrostatic pressure which increased the band gap in similar way as increasing the Al content in Al x Ga 1-x As and suggested that DX centers are can be isolated donors [55]. The term DX becomes common for a donor that has negative-U properties with its negatively charged state DX -lying deeper than the neutral state.…”

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Electron Paramagnetic Resonance studies of negative-U centers in AlGaN and SiC

Trinh¹

2015

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Silicon (Si) is the most commonly used n-type dopant in AlGaN, but the conductivity of Si-doped Al x Ga 1-x N was often reported to drop abruptly at high Al content (x>0.7) and the reason was often speculated to be due to either compensation by deep levels or self-compensation of the so-called DX (or negative-U) center. Understanding the electronic structure of Si and carrier compensation processes is the essential for improving the n-type doping of high-Al-content Al x Ga 1-x N. In our studies of Si-doped AlGaN layers grown by metal-organic chemical vapor deposition, Electron Paramagnetic Resonance (EPR) was used to study the electronic structure of Si in high-Al-content Al x Ga 1-x N.From the temperature dependence of the concentration of the Si donor on the neutral charge state E d determined by EPR, we showed that Si already forms a stable DX center in Al x Ga 1-x N with x ~0.77. However, with the Fermi level locating only ~3 meV below E d , Si still behaves as a shallow donor and high conductivity at room temperature could be achieved in Al 0.77 Ga 0.23 N:Si layers. In samples with the concentration of the residual oxygen (O) impurity larger than that of Si, we observed no carrier compensation by O in Al 0.77 Ga 0.23 N:Si layers, suggesting that at such Al content, O does not seem to hinder the n-type doping in the material. The result is presented in paper 1.In paper 2, we determined the dependence of the E DX level of Si on the Al content in Al x Ga 1-x N:Si layers (0.79≤x≤1) with the Si concentration of ~2×10 18 cm -3 and the concentrations of residual O and C impurities of about an order of magnitude lower (~1÷2×10 17 cm -3 ). We found the coexistence of two DX centers (stable and metastable ones) of Si in Al x Ga 1-x N for x≥0.84. For the stable DX center, abruptly deepening of E DX with increasing of the Al content for x≥0.83 was observed, explaining the drastic decrease of the conductivity as often reported in previous transport studies. For the metastable DX center, the E DX level remains close to E d for x=0.84÷1 (~11 meV for AlN).The Z 1 /Z 2 defect is the most common deep level revealed by Deep Level Transient Spectroscopy (DLTS) in 4H-SiC epitaxial layers grown by chemical vapor deposition (CVD). It has previously been shown by DLTS to be a negative-U system which is more stable with capturing two electrons. The center is also known to be the lifetime killer in asiv grown CVD material and, therefore, attracts much attention. Despite nearly two decades of intensive studies, including theoretical calculations and different experimental techniques, the origin of the Z 1 /Z 2 center remains unclear. EPR is known to be a powerful method for defect identification, but a direct correlation between EPR and DLTS is difficult due to different requirements on samples for each technique. Using high n-type 4H-SiC CVD free-standing layers irradiated with lowenergy (250 keV) electrons, which mainly displace carbon atoms creating C vacancies, C interstitials and their associated defects, it was possible...

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High Pressure Probes of Electronic Structure and Luminescence Properties of Transition Metal and Lanthanide Systems

Bray

2000

Topics in Current Chemistry

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Donor states in GaAs under hydrostatic pressure

Cited by 23 publications

References 46 publications

Anion-Cation Site Dependence of Pressure Coefficients for Donors in GaAs

Anion-Cation Site Dependence of Pressure Coefficients for Donors in GaAs

Electron Paramagnetic Resonance studies of negative-U centers in AlGaN and SiC

High Pressure Probes of Electronic Structure and Luminescence Properties of Transition Metal and Lanthanide Systems

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