| 1. |
- Kakanakova-Georgieva, Anelia, et al.
(författare)
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The complex impact of silicon and oxygen on the n-type conductivity of high-Al-content AlGaN
- 2013
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 102:13, s. 132113-
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Tidskriftsartikel (refereegranskat)abstract
- Issues of major relevance to the n-type conductivity of Al0.77Ga0.23N associated with Si and O incorporation, their shallow donor or deep donor level behavior, and carrier compensation are elucidated by allying (i) study of Si and O incorporation kinetics at high process temperature and low growth rate, and (ii) electron paramagnetic resonance measurements. The Al0.77Ga0.23N composition correlates to that Al content for which a drastic reduction of the conductivity of AlxGa1−xN is commonly reported. We note the incorporation of carbon, the role of which for the transport properties of AlxGa1−xN has not been widely discussed.
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| 2. |
- Kakanakova-Gueorguie, Anelia, et al.
(författare)
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n-Type conductivity bound by the growth temperature: the case of Al0.72Ga0.28N highly doped by silicon
- 2016
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Ingår i: Journal of Materials Chemistry C. - : ROYAL SOC CHEMISTRY. - 2050-7526 .- 2050-7534. ; 4:35, s. 8291-8296
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Tidskriftsartikel (refereegranskat)abstract
- High-Al-content AlxGa(1-x)N layers, x similar to 0.72, have been grown by metal organic chemical vapour deposition (MOCVD) at a temperature ranging from 1000 to 1100 degrees C, together with high flow rate of the dopant precursor silane (SiH4) in order to obtain highly Si-doped Al0.72Ga0.28N layers, similar to 1 x 10(19) cm(-3) as measured by secondary ion mass spectrometry (SIMS). Further characterization of the layers by capacitance-voltage (C-V), electron paramagnetic resonance (EPR), and transmission electron microscopy (TEM) measurements reveals the complex role of growth temperature for the n-type conductivity of high-Al-content AlxGa1-xN. While increasing temperature is essential for reducing the incorporation of carbon and oxygen impurities in the layers, it also reduces the amount of silicon incorporated as a donor.
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| 3. |
- Kakanakova-Gueorguie, Anelia, et al.
(författare)
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Silicon and oxygen in high-Al-content AlGaN: incorporation kinetics and electron paramagnetic resonance study
- 2014
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Ingår i: Gettering and Defect Engineering in Semiconductor Technology XV. - : Trans Tech Publications Inc.. ; , s. 441-445
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Konferensbidrag (refereegranskat)abstract
- The high-Al-content AlxGa1-xN alloys, xgreater than0.70, and AlN is the fundamental wide-band-gap material system associated with the technology development of solid-state LEDs operating at the short wavelengths in the deep-UV (lambda less than 280 nm). Yet, their properties are insufficiently understood. The present study is intended to bring elucidation on the long-time debated and much speculated Si transition from shallow donor in GaN to a localized deep DX defect in AlxGa1-xN alloys with increasing Al content. For that purpose electron paramagnetic resonance is performed on a particular selection of high-Al-content epitaxial layers of Al0.77Ga0.23N, alternatively Al0.72Ga0.28N, alloy composition.
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| 4. |
- Kawahara, Koutarou, et al.
(författare)
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Investigation on origin of Z(1/2) center in SiC by deep level transient spectroscopy and electron paramagnetic resonance
- 2013
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Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 102:11
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Tidskriftsartikel (refereegranskat)abstract
- The Z(1/2) center in n-type 4H-SiC epilayers-a dominant deep level limiting the carrier lifetime-has been investigated. Using capacitance versus voltage (C-V) measurements and deep level transient spectroscopy (DLTS), we show that the Z(1/2) center is responsible for the carrier compensation in n-type 4H-SiC epilayers irradiated by low-energy (250 keV) electrons. The concentration of the Z(1/2) defect obtained by C-V and DLTS correlates well with that of the carbon vacancy (V-C) determined by electron paramagnetic resonance, suggesting that the Z(1/2) deep level originates from V-C.
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| 5. |
- Kawahara, Koutarou, et al.
(författare)
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Quantitative comparison between Z1∕2 center and carbon vacancy in 4H-SiC
- 2014
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Ingår i: Journal of Applied Physics. - : American Institute of Physics (AIP). - 0021-8979 .- 1089-7550. ; 115:14, s. 143705-
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Tidskriftsartikel (refereegranskat)abstract
- In this study, to reveal the origin of the Z(1/2) center, a lifetime killer in n-type 4H-SiC, the concentrations of the Z(1/2) center and point defects are compared in the same samples, using deep level transient spectroscopy (DLTS) and electron paramagnetic resonance (EPR). The Z(1/2) concentration in the samples is varied by irradiation with 250 keV electrons with various fluences. The concentration of a single carbon vacancy (V-C) measured by EPR under light illumination can well be explained with the Z(1/2) concentration derived from C-V and DLTS irrespective of the doping concentration and the electron fluence, indicating that the Z(1/2) center originates from a single V-C.
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| 6. |
- Mehnke, Frank, et al.
(författare)
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Electronic properties of Si-doped AlxGa1-xN with aluminum mole fractions above 80%
- 2016
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Ingår i: Journal of Applied Physics. - : AMER INST PHYSICS. - 0021-8979 .- 1089-7550. ; 120:14
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Tidskriftsartikel (refereegranskat)abstract
- The dependence of the activation energy as well as the energetic levels of the neutral charge state and the DX center of the Si donor in AlxGa1-xN: Si samples on aluminum content and SiH4/III ratio were investigated by electron paramagnetic resonance (EPR) measurements, Van-der-Pauw resistivity measurements, and Hall-effect measurements. It was found by EPR measurements that the energy distance of the neutral charge state of the Si donor from the conduction band increases with increasing aluminum content from 61 meV for x = 0.82 to 106 meV for x = 0.89. Additionally, the formation of a DX center below the neutral charge state which is deepening from 6 meV for x = 0.82 to 58 meV for x = 0.89 is observed. This results in a linearly increasing activation energy with increasing aluminum content from 67 meV for x = 0.82 to 164 meV for x = 0.89. This is consistent with the activation energies as determined by Hall-effect measurements showing a linear increase from 24 meV for x = 0.85 to 211 meV for x = 0.96, as well as the activation energies as determined by Van-der-Pauw resistivity measurements. By varying the SiH4/III ratio we observed a formation of a minimum resistivity in accordance with the room temperature charge carrier density. However, no clear dependence of the activation energy was observed. EPR measurements of samples with a high SiH4/III ratio hint to an increased incorporation probability of a deep secondary donor species which might explain the increase in resistivity. Published by AIP Publishing.
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| 7. |
- Nakane, Hiroki, et al.
(författare)
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Deep levels related to the carbon antisite-vacancy pair in 4H-SiC
- 2021
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Ingår i: Journal of Applied Physics. - : American Institute of Physics (AIP). - 0021-8979 .- 1089-7550. ; 130:6
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Tidskriftsartikel (refereegranskat)abstract
- Photo-induced current transient spectroscopy (PICTS) and electron paramagnetic resonance (EPR) are used to study irradiation-induced defects in high-purity semi-insulating (HPSI) 4H-SiC. Several deep levels with the ionization energy ranging from 0.1 to similar to 1.1 eV have been observed in irradiated and annealed samples by PICTS. Among these, two deep levels, labeled E370 and E700 at similar to 0.72 and similar to 1.07 eV below the conduction band, respectively, are detected after high-temperature annealing. The appearance and disappearance of these two deep levels and the EPR signal of the positive C antisite-vacancy pair (CSiVC+) in the sample annealed at 1000 and 1200 degrees C, respectively, are well correlated. Based on data from PICTS and EPR and the energies predicted by previous calculations for different charge states of dominant intrinsic defects, the E370 and E700 levels are suggested to be related to the charge transition levels (0|-) and (+|0), respectively, of the C antisite-vacancy pair. The activation energy of E-a similar to 1.1 eV in commercial HPSI 4H-SiC materials is, therefore, reassigned to be related to the single donor (+|0) level of CSiVC.
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| 8. |
- Nilsson, Daniel, et al.
(författare)
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Highly Si-doped Al0.72Ga0.28N layers: n-type conductivity bound by the process temperature
- 2014
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Establishing n- and p- type conductivity via intentional doping in epitaxial layers is fundamental to any semiconductor material system and its relevant device applications. Process parameters such as temperature, precursor gas-flow-rates and pressure may all control intentional doping in metal-organic chemical vapour deposition (MOCVD) of semiconductor materials. The incorporation of impurities such as carbon and oxygen may also be affected by the same process parameters, and the concentration of these impurities has a direct impact on the electrical, optical and thermal properties of epitaxial layers, as has been observed in the MOCVD of technologically-important III-V semiconductor materials such as AlGaAs and GaN.
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| 9. |
- Nilsson, Daniel, et al.
(författare)
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On the behavior of the silicon donor in conductive AlxGa1-xN (0.63≤x≤1) layers
- 2015
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Ingår i: Physica status solidi. B, Basic research. - : Wiley-VCH Verlagsgesellschaft. - 0370-1972 .- 1521-3951. ; 252:6, s. 1306-1310
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Tidskriftsartikel (refereegranskat)abstract
- We have studied the silicon donor behavior in intentionally silicon doped AlxGa1-xN (0.63≤x≤1) grown by hot-wall metal-organic chemical vapor deposition. Efficient silicon doping was obtained for lower Al contents whereas the conductivity drastically reduces for AlGaN layers with Al content in the range x~0.84-1. Degradation of the structural quality and compensation by residual O and C impurities were ruled out as possible explanations for the reduced conductivity. By combining frequency dependent capacitance-voltage and electron paramagnetic resonance measurements we show that the Si donors are electrically active and that the reduced conductivity can be explained by the increased activation energy caused by the sharp deepening of the Si DX– state..
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| 10. |
- Son Tien, Nguyen, et al.
(författare)
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Electron paramagnetic resonance and theoretical studies of Nb in 4H- and 6H-SiC
- 2012
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Ingår i: Journal of Applied Physics. - : American Institute of Physics (AIP). - 0021-8979 .- 1089-7550. ; 112:8, s. 083711-
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Tidskriftsartikel (refereegranskat)abstract
- High purity silicon carbide (SiC) materials are of interest from high-power high temperature applications across recent photo-voltaic cells to hosting solid state quantum bits, where the tight control of electrically, optically, and magnetically active point defects is pivotal in these areas. 4H- and 6H-SiC substrates are grown at high temperatures and the incorporation of transition metal impurities is common. In unintentionally Nb-doped 4H- and 6H-SiC substrates grown by high-temperature chemical vapor deposition, an electron paramagnetic resonance (EPR) spectrum with C-1h symmetry and a clear hyperfine (hf) structure consisting of ten equal intensity hf lines was observed. The hf structure can be identified as due to the interaction between the electron spin S - 1/2 and the nuclear spin of Nb-93. Additional hf structures due to the interaction with three Si neighbors were also detected. In 4H-SiC, a considerable spin density of similar to 37.4% was found on three Si neighbors, suggesting the defect to be a complex between Nb and a nearby carbon vacancy (V-C). Calculations of the Nb-93 and Si-29 hf constants of the neutral Nb on Si site, Nb-Si(0), and the Nb-vacancy defect, NbSiVC0, support previous reported results that Nb preferentially forms an asymmetric split-vacancy (ASV) defect. In both 4H- and 6H-SiC, only one Nb-related EPR spectrum has been observed, supporting the prediction from calculations that the hexagonal-hexagonal defect configuration of the ASV complex is more stable than others.
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