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Two self-doped conjugated polyelectrolytes, having semiconducting and metallic behaviors, respectively, have been blended from aqueous solutions in order to produce materials with enhanced optical and electrical properties. The intimate blend of two anionic conjugated polyelectrolytes combine the electrical and optical properties of these, and can be tuned by blend stoichiometry. In situ conductance measurements have been done during doping of the blends, while UV−vis and EPR spectroelectrochemistry allowed the study of the nature of the involved redox species. We have constructed an accumulation/depletion mode organic electrochemical transistor whose characteristics can be tuned by balancing the stoichiometry of the active material.

The carbon vacancy (V C ) has been suggested by different studies to be involved in the Z 1 /Z 2 defect-a carrier lifetime killer in SiC. However, the correlation between the Z 1 /Z 2 deep level with V C is not possible since only the negative carbon vacancy (V − C ) at the hexagonal site, V − C (h), with unclear negative-U behaviors was identified by electron paramagnetic resonance (EPR). Using freestanding n-type 4H -SiC epilayers irradiated with low energy (250 keV) electrons at room temperature to introduce mainly V C and defects in the C sublattice, we observed the strong EPR signals of V − C (h) and another S = 1/2 center. Electron paramagnetic resonance experiments show a negative-U behavior of the two centers and their similar symmetry lowering from C 3v to C 1h at low temperatures. Comparing the 29 Si and 13 C ligand hyperfine constants observed by EPR and first principles calculations, the new center is identified as V − C (k). The negative-U behavior is further confirmed by large scale density functional theory supercell calculations using different charge correction schemes. The results support the identification of the lifetime limiting Z 1 /Z 2 defect to be related to acceptor states of the carbon vacancy.

Deep levels by proton and electron irradiation in 4H-SiC J. Appl. Phys. 98, 053706 (2005);Vacancies and deep levels in electron-irradiated 6H SiC epilayers studied by positron annihilation and deep level transient spectroscopyThe 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 . V C 2013 American Institute of Physics. [http://dx.

Electron paramagnetic resonance studies of Si-doped AlxGa1−xN (0.79 ≤ x ≤ 1.0) reveal two Si negative-U (or DX) centers, which can be separately observed for x ≥ 0.84. We found that for the stable DX center, the energy |EDX| of the negatively charged state DX−, which is also considered as the donor activation energy, abruptly increases with Al content for x ∼ 0.83–1.0 approaching ∼240 meV in AlN, whereas EDX remains to be close to the neutral charge state Ed for the metastable DX center (∼11 meV below Ed in AlN).

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.

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

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