A Comparative Study on the Effect of Optical Illumination on Si1-xGex and Si based DDR IMPATT Diodes at W-Band

The effect of optical illumination on DC and dynamic performance of Si1-xGex based double drift region (DDR) (p+pnn+) IMPATT diode operating at W-Band is investigated and compared with its Silicon counterpart. Top Mounted (TM) and Flip Chip (FC) structures are chosen and the composition of photocurrent is altered by shining light on the p+ side and n+ side of the device through optical windows. A double iterative computer simulation method based on drift-diffusion model has been used to study the small signal performance and subsequent modification of the small signal parameters owing to optical illumination. The role of leakage current in controlling the dynamic properties is studied by varying the current multiplication factors for electrons (Mn) and for holes (Mp). It is observed that both the DC and small signal parameters of both the diodes are affected significantly due to optical illumination. Under optical illumination of the device, the frequency shift is observed to be more upwards upon lowering of Mn than lowering of Mp for both the diodes. The frequency chirping in both Si1-xGex and Si IMPATTs are found to be of the order of few GHz, thereby indicating their high photo-sensitiveness at W-Band. But the results significantly indicates that photo-sensitiveness of Si1-xGex IMPATT is much greater than the Si IMPATT; which is one of the major findings of this work.