Porous SiC (P-SiC), is presently being investigated as a buffer layer for epitaxial SiC and GaN growth, an active layer for gas sensors, and a cell-friendly transistor for in vivo applications. Recently, a correlation between carrier concentration and pore density in n-type P-SiC has been observed, and this observation has been interpreted to mean that pores can act as electron traps. Traps in semiconductors can be conveniently studied by deep level transient spectroscopy (DLTS), and we have applied this technique to P-SiC. In comparison with the nonporous SiC case, most of the traps are the same, and indeed are common to various SiC materials studied by other workers in the past. However, we also find a new trap of very high concentration (~ 6 x 10¹⁷ cm^-3), appearing only in P-SiC. The DLTS signal from this new trap displays abnormally slow and non-exponential saturation with filling pulse length (t_p), whereas most traps saturate rapidly and exponentially. Besides the unusual saturation behavior, the DLTS emission spectrum moves to higher temperatures as t_p increases, and also narrows with t_p. The standard DLTS modeling framework cannot explain these observances. It should be noted that similar effects have been observed in various semiconductors in which the traps lie along vertical threading dislocations, and thus form line charges. In this work, we present a single, general formalism that describes both capture and emission behavior for traps that exist on the inner surfaces or interfaces of spherical or cylindrical structures imbedded in semiconductor materials. Common structures of these shapes include pores, precipitates, and nanopipes. A very important case is cylindrical nanopipes (open-core screw dislocations) in GaN grown on Al₂O₃, which can sometimes generate states in the band gap, either due to dangling bonds or impurities that congregate nearby (the Cottrell atmosphere). Here, we will model dislocations in GaN as well as nanopores in SiC.

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