Recombination Processes Controlling the Carrier Lifetime in n(-)4H-SiC Epilayers with Low Z sub 1/2 Concentrations
NAVAL RESEARCH LAB WASHINGTON DC
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The dominant recombination processes controlling the carrier lifetime in n-type 4H SiC epitaxial layers grown with low concentrations of the Z12 defect the dominant bulk lifetime killer, where Z12 no longer determines the lifetime, have been investigated by studying the variation in the carrier lifetime with temperature. The temperature dependent lifetimes were obtained primarily by low-injection photoluminescence decay for several low-Z12 epilayers over a wide temperature range. The results were fitted to simulations of the temperature dependent recombination rate, where bulk, surface and interface recombination was considered. No significant contribution from other bulk defects was observed, and upper limits to the bulk recombination rate were found to be consistent with the low Z12 concentrations measured in these materials. There was also no significant contribution from carrier capture at the epilayersubstrate interface, which is consistent with behavior expected at low injection for low-doped epilayers grown on n substrates. Corresponding high-injection measurements exhibited very different behavior, consistent with the surfaceinterface under flat-band conditions. Consequently, it is concluded that for low-Z12 materials, control of the carrier lifetime has not been transferred from Z12 to another bulk defect, but is instead dominated by surface and interface recombination. Simulations suggest that further enhancement of the total lifetime under the high injection conditions of a device structure would require very thick epilayers, effectively passivated surface and interface recombination and a further reduction in the remaining Z12 concentrations. The temperature dependence of the low-injection carrier lifetime was also found to provide a method to estimate the surface band bending and the surface defect density.
- Inorganic Chemistry