P-type Si-Si0.2Ge0.8 superlattices prepared on Si0.5Ge0.5-relaxed buffer substrates are promising structures for the development of SiGe quantum cascade lasers. To explore the resonant tunneling in this system, we studied the vertical transport in Si-Si0.2Ge0.8 superlattices. Low-temperature molecular beam epitaxy enables growth of highly uniform and relatively thick (similar to0.5 mum) superlattices with strain symmetrized design. The sample with 8.3-nm thick Si0.2Ge0.8 quantum wells and 5-nm thick Si barriers exhibited a series of sharp resonant tunneling peaks and negative differential conductance. A signature of electric field domain formation was also found. By reducing the Si-barrier thickness to 3 nm and also reducing the quantum well thickness to 5 nm, only a single peak was observed, but the resonant tunneling peak is about a factor of 2 enhanced compared to the sample with thicker barriers. (C) 2003 Elsevier B.V. All rights reserved.