Strained Si/Si1−yCy superlattice based quasi-read avalanche transit-time devices for terahertz ultrafast switches

Abstract

Effects of selective carbon (C) incorporation in silicon (Si) quasi-read-avalanche-transit-time (QRATT) devices are studied through indigenously developed non-linear Strain-corrected-mixed-quantum-tunneling-drift–diffusion-model (SMQTDDM). A superlattice with alternate thin films of strained-Si and comparatively thick layers of Si0.99C0.01 stressors constitutes the active region. Out-of-plane mobility enhancement occurs due to the in-plane biaxial strain at Si/Si0.99C0.01 interfaces. Band offset between Si/Si0.99C0.01results in high injection velocity. Combined effect of strain-engineering and band offset amounts to the application of periodic accelerating pulse along the active region. This subsequently reduces carrier transit-time and results in THz oscillation in Si-ATT-diode. Remarkable RF performance (RF-power ~ $$23.2\times {10}^{8}$$ W/m2 at 0.73 THz) of exotic Si-QRATT-devices is reported for the first time. The simulation incorporates quantum-effects, process-induced-strain, parasitic-resistance, thermal-model and inter-sub-band-tunneling in the dispersion relation of the multiple-quantum-wells through a combined solution of Schrodinger–Poisson equations. The theoretical analysis is verified with experimental observations for in-house-fabricated Si-ATT-diodes. QRATT-device-based THz series-shunt switches are further explored.