Effect of Mobile Space Charge in Si/Si0.9Ge0.1 Heterojunction Double Drift Impart Oscillator at W-Band Window Frequency

Abstract

Studies on mobile space charge effect in the depletion layer of heterojunction Si/Si0.9Ge0.1 IMPATT diode (p + pnn + structure with p + = Si1-xGex, p = Si1-xGex, n = Si and n + = Si; mole fraction x = 0.1) has been simulated at 94 GHz window frequency. The simulation study based on drift-diffusion model for the study of DC, high frequency and negative resistivity properties of the device at different bias current densities has been carried out. The maximum DC-to-millimeter wave conversion efficiency of 14.82% is obtained at a bias current density of 0.7  10 8 A/m 2 . Si/Si1-xGex DDR Impatts is found to give peak negative conductance at about 92 GHz (close to 94 GHz design window frequency) for a bias current density of 0.7  10 8 A/m 2 . The device performance degrades with mobile space charge effect at bias current densities exceeding 2.0  10 8 A/m 2 . Hence bias current density up to 2  10 8 A/m 2 may be considered as the limit to realize high efficiency with high power from the