Performance Optimization of 3-gain-stage InGaAs/InAlAs Avalanche Photodetector

We constructed a 3-gain-stage InGaAs/InAlAs avalanche photodiode device model through numerical simulation calculations based on the gain-noise mechanism. The absorption layer and grading layer are optimized respectively. The performance of the device is improved by using a partially depleted absorption layer and optimizing the thickness of the grading layer under the condition of determining the proportion of the partially depleted absorption layer. Compared with the single absorption layer, the partially depleted absorption layer structure adopted in the absorption layer can improve the gain of the device more significantly at low doping concentration than at high doping concentration. With the increase of the total doping concentration in the absorption layer, the energy band gradually increases, which can reduce the dark current in the absorption layer. Therefore, it is necessary to choose an appropriate doping concentration. The addition of grading layer between the charge layer and the absorption layer can avoid the accumulation of holes in the charge layer, reduce the number of minority carriers’ recombination in the charge layer, and maintain the control effect of the charge layer on the device’s electric field. Moderately increasing the thickness of the grading layer can share part of the absorption layer voltage, and reduce the dark current of the device while ensuring the number of photogenerated electrons drifting to the charge layer. The results show that when the partially depleted absorption layer is ωa1 : ωa2 = 1 : 1 and the grading layer thickness is ωg = 100 nm, the maximum 3-gain-stage device’s gain can reach 150. The optimized structure can provide design and optimization ideas for more stages of avalanche photodiode to increase the gain and reduce the excess noise.