Hole tunnelling properties in resonant tunnelling diodes with Si/strained Si_0.8Ge_0.2 heterostructures grown on Si(1 0 0) by low-temperature ultraclean LPCVD

Hole resonant tunnelling diodes (RTDs) with Si/strained Si _1-xGe_x heterostructures epitaxially grown on Si(1 0 0) were fabricated, and sharp current peaks have been reproducibly observed. From the quantum well width dependence of the current-voltage characteristics, at the peak voltage, heavy holes in the accumulation region resonantly tunnel through the estimated resonant states of a light hole and a heavy hole in a Si_1-xGe_x quantum well. The top contact and mesa area dependence of the peak current shows that the tunnel current only flows under a top contact electrode, i.e. the leakage current at the sidewall is negligibly small. The resonant tunnelling current density reaches as high as 3.6 kA cm^-2 at 0.19 V with 2 nm thick barriers. Moreover, the introduction of higher Ge fraction effectively suppresses the increase of the valley current and enables negative differential conductance at higher operation temperature.