Optimization of the Linearity of InGaAs/InAlAs SAGCM APDs

Linearity is of utmost importance for avalanche photodiodes (APDs) used in communication systems for Ethernet beyond 10 Gbit/s. APDs with high linearity are able to extend the transmission distance without additional power consumption, but the linearity has not been investigated in detail. In this paper, a model of the InGaAs/InAlAs separate absorption, grading, charge and multiplication (SAGCM) APD is established to optimize the linearity parameters in the device. The simulated results show that the grading layer and the charge layer are critical for the linearity and by reducing the thickness or the doping concentration of the grading layer, the linearity can be improved. Besides, a thick absorption layer improves the quantum efficiency while degrades the linearity. A thin multiplication layer improves the linearity.