Photoinduced transient spectroscopy of defect centers in GaN and SiC

Compensating defect centres in semi-insulating 6H-SiC

“…The mechanism responsible for the occurrence of the negative amplitude of the photocurrent relaxation waveforms has not been until now fully understood. However, there are some results allowing for explanation of this phenomenon [13,14]. They indicate that the negative amplitude of the re− laxation waveform can result from the specific change in the occupancy of a defect level involved in the material com− pensation.…”

“…As a result, the activation energy E a and the pre−exponential factor A, related to the capture cross− −section, are calculated for detected defect centres. Because of the implementation of advanced signal processing tech− niques [13,15], the PITS technique sensitivity is high being of the order of 1×10 13 cm -3 . In the case of this technique, however, the determination of trap concentration is not as straightforward as in the deep level transient capacitance spectroscopy (DLTS).…”

“…For further processing, each photocurrent relaxation waveform was normalized with respect to the photocurrent amplitude at the end of the UV pulse. The detailed descrip− tion of the experimental setup dedicated to characterization of defect centres in SI wide bangap materials has been pre− sented elsewhere [13].…”

High‐resolution photoinduced transient spectroscopy of defect centres in semi‐insulating GaP

“…When retrapping of the charge carriers by the defect centres is neglected, the part of the photocurrent relaxation waveforms with a time constant longer than ~1 µs is related to the thermal emission of charge carriers and the reciprocal of this time constant is equal to the emission rate [4]. The images of experimental spectral fringes are obtained by means of the twodimensional analysis of the photocurrent relaxation waveforms using the correlation procedure and the numerical procedure based on the inverse Laplace transform algorithm (ILT) [4,5]. As a result, the temperature changes in the time constants of the relaxation waveforms are visualized in the 3D space as the spectral surface being a function of two variables: the temperature (T) and emission rate (e T ).…”

“…The electronic properties of defect centres in the semiinsulating wafers A and B were investigated by means of the high-resolution photoinduced transient spectroscopy (HRPITS) implemented in the intelligent measuring system described elsewhere [4,5]. Before the measurements, arrays of two co-planar ohmic contacts were made by evaporating a 20-nm layer of Cr and a 300-nm layer of Au on the mirror-polished surface of the wafers followed by rapid thermal annealing at 350 o C. The width of the gap between two co-planar contacts was 0.7 mm.…”