Papers by Keyword: Photoconductivity Decay

Abstract: The quality of the epitaxial layer plays an important role in the performance of modern power electronic devices. Minority carrier lifetime is known to be sensitive to defects like dislocations, stacking faults, and points defects. Therefore, in this work lifetime measurements by microwave detected photoconductivity decay are used to evaluate the quality of the epitaxial layer on various 4H-SiC substrates from different vendors. The stability of the measurement technique is shown by a daily release measurement. This allows for a reliable analysis of almost 300 typical 1,200 V epilayer stacks. It has been shown that the effective lifetime of these samples can be separated into two different ranges. The lifetime values of about 120 ns fit to theoretical calculations. The cause for the increased lifetime of about 250 ns in the second range has yet to be determined in further research. Furthermore, the lifetime maps were used to locate defects in the surface near regions.

Abstract: Among all the material parameters of a semiconductor, the lifetime of the carriers is one of the most complex, as it is a function of the dominant recombination mechanism, the number of carriers, the structural parameters and the temperature. Nevertheless, the lifetime of the carriers is a very useful and fundamental parameter to be determined for the qualification of the semiconductor in order to allow the improvement of the manufacturing process and the optimization of the operation of the semiconductor device. Thus being strongly linked to many physical and electronic parameters, the lifetime of the carriers cannot be provided only with a theoretical average value and an experimental measured value must be obtained. In the case of semiconductor junctions, precise measurements of the open-circuit voltage decay, OCVD, make it possible to trace the lifetime of the carriers through the device. An automated method for OCVD measurements presented in this contribution overcomes the main limitations that arise in the standard method when used for the characterization of the lifetime of carriers as it achieves the "open circuit conditions" of the device under test and reduces inherent noise of the differential operation mode of the method.

Abstract: We measured the excess carrier lifetimes in as-grown and electron irradiated p-type 4H-SiC epitaxial layers with the microwave photoconductivity decay (-PCD) method. The carrier lifetime becomes longer with excitation density for the as-grown epilayer. This dependence suggests that e ≥h for the dominant recombination center, where e andh are capture cross sections for electrons and holes, respectively. In contrast, the carrier lifetime does not depend on the excitation density for the sample irradiated with electrons at an energy of 160 keV and a dose of 1×1017 cm-2. This may be due to the fact that recombination centers with e <<h were introduced by the electron irradiation or due to the fact that the acceptor concentration was decreased significantly by the irradiation.