APPLICATION OF OPEN CIRCUIT VOLTAGE DECAY TO THE CHARACTERIZATION OF EPITAXIAL LAYER

Milan Ťapajna - Jaroslav Pjenčák - Andrej Vrbický - Ladislav Harmatha - Pavol Kúdela

   High quality silicon epitaxial layers are inevitable in bipolar and/or unipolar technology. However, their properties are not as easy characterized as those of bulk material. The recombination lifetime is dominated by surface/interface recombination for thin layers, which epitaxial ones generally are. We have designed a diode structure with n⁺np⁺ and p⁺pn⁺ epitaxial layers for the open circuit voltage decay (OCVD) technique. In such a structure injected carriers are constrained within the lightly doped base by potential barriers of the junction and high-low contact and their concentration can then decrease only by recombination. Performing OCVD measurement for high-level injection condition, also τ_n and τ_p could be evaluated. The carrier lifetime obtained in this manner yields information mainly about the defect properties of the epitaxial layer, nevertheless, surface/interface recombination can strongly influence the entire recombination process. This phenomenon is also discussed and a simple technique for separation between bulk and interface recombination is proposed.

Keywords: OCVD, carrier lifetime, epitaxial layer characterization, interface recombination

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