High PVCR Si/Si 1−xGe x DW RTD formed with new triple-layer buffer

Abstract

A new thin triple-layer buffer consisting of three SiGe alloy layers is proposed for Si/Si 1− x Ge x resonant tunneling diodes (RTDs). The triple-layer buffer is compared to our previously proposed thin double-layer buffer with x being stepwise increased. The triple-layer buffer is formed by inserting an ultra-thin high Ge composition SiGe alloy layer between Si substrate and the thin double-layer buffer. By insertion of the ultra-thin high Ge composition SiGe alloy layer, the triple-layer buffer is more relaxed; however, the relaxation rate is limited to around 50% under our experimental conditions. Although the triple-layer buffer has still strain and the barrier height is relatively low, a double-well RTD using this buffer exhibits a peak-to-valley current ratio (PVCR) of as high as ∼50 000, which is far larger than that of standard III–V RTDs. The results also indicate that the proposed buffer leads to a high crystalline quality quantum well structure and that inelastic electron scattering in the Si/Si 1− x Ge x RTD is inherently low.