Stable and metastable Si negative-U centers in AlGaN and AlN

Trinh, Xuan Thang; Nilsson, Daniel; Ivanov, Ivan Gueorguiev; Janzén, Erik; Kakanakova‐Georgieva, Anelia; Són, Nguyên Tiên

doi:10.1063/1.4900409

Cited by 54 publications

(44 citation statements)

References 30 publications

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“…Such a temperature dependence of n(T) is typical for a negative-U donor, often called a DX center, similar to the behavior of the Si donor in high-Al-content AlGaN. 22 In a DX center, the donor in the neutral charge state Ed prefers to capture a second electron to pair off the spins and undergoes a large lattice relaxation to reduce its energy. 25 At low temperatures, the donors are mainly in the negative charge state DX − , which lies below Ed and is EPR inactive with the electron spin S=0.…”

Section: (A)mentioning

confidence: 99%

“…We show that in partly activated materials with the spin density in the mid 10 16 cm -3 ranges or below, the donor behaves as a negative-U (or DX) center, similar to the Si donor in high-Al-content AlGaN, 22 while in fully activated samples, donor electrons become delocalized and the transformation from isolated donor states to corresponding impurity bands occurs, reducing the donor activation energy. In Section III.…”

Section: Introductionmentioning

confidence: 99%

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Electronic properties of the residual donor in unintentionally doped β-Ga2O3

Són

Goto

Nomura

et al. 2016

Journal of Applied Physics

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Electron paramagnetic resonance (EPR) was used to study the donor that is responsible for the n-type conductivity in unintentionally doped (UID) β-Ga2O3 substrates. We show that in asgrown material, the donor requires high temperature annealing to be activated. In partly activated material with the donor concentration in the 10 16 cm -3 range or lower, the donor is found to behave as a negative-U center (often called a DX center) with the negative charge

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Section: (A)mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Electronic properties of the residual donor in unintentionally doped β-Ga2O3

Són

Goto

Nomura

et al. 2016

Journal of Applied Physics

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“…In many cases, identification of point defects in semiconductors needs additional help from theoretical modeling of the defect. In some cases, the position of the energy level of a point defect can be determined by photoexcitation EPR (photo-EPR) [42,100] or temperature dependence of the EPR signal [23,24,96]. To this end, EPR is a powerful method for identification and characterization of point defects in semiconductors.…”

Section: The a Tensormentioning

confidence: 99%

“…In such case, the observation of the EPR signal of the negative-U center requires thermal energy at elevated temperatures or illumination to increase the population on the unpaired electron state. When the paired electron state lies only a few meV below the unpaired electron state, the population of the unpaired electron state at low temperatures in darkness can be detectable by EPR [23,24].…”

Section: Carrier Lifetime In Sicmentioning

confidence: 99%

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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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Optical signatures of silicon and oxygen related DX centers in AlN

Thonke

Lamprecht

Collazo

et al. 2017

Phys. Status Solidi A

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Bulk AlN crystals typically contain high concentrations of oxygen, silicon, and carbon À as also state-of-the art epitaxial layers typically do, depending on the specific growth conditions. In optical spectroscopy, such crystals show broad bands in the region from 2-5 eV in absorption and emission. We investigated several emission bands in the range from 1.4 to 1.9 eV, especially those centred at 2.0 and 2.4 eV, which under below-bandgap excitation with a 325 nm laser dominate the photoluminescence (PL) spectra both at low and at room temperature. We find clear indications that all these transitions occur between different states of the shallow donors Si or O, and deep acceptors. The donors undergo lattice relaxation and form DX centres. Depending on temperature, the initial state is either a long-lived (S ¼ 1) DXcentre state of the donors, a shallow EMT-like conventional donor state, or a free electron À with markedly different relaxation times for the optical transitions under below-bandgap excitation. The acceptor involved in these PL bands is likely linked to aluminum vacancies. Based on our data, we develop configuration coordinate diagrams and a combined level scheme for multiple transitions in the range from 1.4 to 2.4 eV.Tentative level scheme for PL bands observed in AlN in the range from 1.4 to 2.4 eV.

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Stable and metastable Si negative-U centers in AlGaN and AlN

Cited by 54 publications

References 30 publications

Electronic properties of the residual donor in unintentionally doped β-Ga2O3

Electronic properties of the residual donor in unintentionally doped β-Ga2O3

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

Optical signatures of silicon and oxygen related DX centers in AlN

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