Deep level defects in 4H-SiC Schottky barrier diodes (SBDs) fabricated on n-type epitaxial 4H-SiC have been identified by thermally stimulated capacitance (TSCAP) spectroscopy prior to and after 60Co-gamma irradiation. The TSCAP measurements on the non-irradiated SBDs reveal two electron traps at Ec-0.63 eV (∼250 K) and Ec-1.13 eV (∼525 K), whereas only one trap at Ec-0.63 eV is identified by conventional thermally stimulated current (TSC) measurements. Hence, TSCAP spectroscopy is more effective in identifying deep level defects in epitaxial 4 H-SiC SBDs as compared to the TSC spectroscopy. Upon exposure to 60Co-gamma rays up to a dose of 100 Mrad, significant changes in the concentration of the traps at Ec-0.63 eV, Ec-1.13 eV, and one new trap at Ec-0.89 eV (∼420 K) are observed. The electrical characteristics of the SBDs are considerably changed after gamma irradiation. The dominant mechanisms responsible for the irradiation induced changes in the SBD electrical characteristics are analyzed by incorporating the trap signatures in the commercial Silvaco® TCAD device simulator. The extracted trap parameters of the irradiated SBDs may be helpful in predicting the survival of 4H-SiC SBD detectors at higher irradiation levels.
Real-time photoplethysmogram (PPG) denoising and data compression has become most essential requirements for accurately measuring vital parameters and efficient data transmission but that may introduce different kinds of waveform distortions due to the lossy processing techniques. Subjective quality assessment tests are the most reliable way to assess the quality, but they are time expensive and also cannot be incorporated with quality-driven compression mechanism. Thus, finding a best objective distortion measure is highly demanded for automatically evaluating quality of reconstructed PPG signal that must be subjectively meaningful and simple. In this paper, we present four types of objective distortion measures and evaluate their performance in terms of quality prediction accuracy, Pearson correlation coefficient and computational time. The performance evaluation is performed on different kinds of PPG waveform distortions introduced by the predictive coding, compressed sampling, discrete cosine transform and discrete wavelet transform. On the normal and abnormal PPG signals taken from five standard databases, evaluation results showed that different subjective quality evaluation groups (5-point, 3-point and 2-point rating scale) had different best objective distortion measures in terms of prediction accuracy and Pearson correlation coefficient. Moreover, selection of a best objective distortion measure depends upon type of PPG features that need to be preserved in the reconstructed signal.
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