Resonant tunneling in Si–SiGe superlattices on relaxed buffer substrates

Abstract

P-type Si–Si 0.2Ge 0.8 superlattices prepared on Si 0.5Ge 0.5-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–Si 0.2Ge 0.8 superlattices. Low-temperature molecular beam epitaxy enables growth of highly uniform and relatively thick (∼0.5 μm) superlattices with strain symmetrized design. The sample with 8.3-nm thick Si 0.2Ge 0.8 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.