Objective InGaAs materials as absorption layers and Si materials as multiplication layers are potential alternatives for achieving highperformance avalanche photodiodes (APDs). However, simple and wellperforming InGaAs/Si APDs are difficult to fabricate owing to the 7.7% lattice mismatch between InGaAs and Si. Investigators have recently reported that a -Si was introduced at the InGaAs/Si APD bonding interface to inhibit the nucleation of mismatch dislocations and realize an ultralow dark current. However, owing to the large bandgap of a -Si, the bonding interface has a large conduction band and valence band offset. This causes the gain of the device to decrease. Ge and Si are both indirect band gap semiconductors, and Ge materials have the advantages of a small gap width and a long absorption cutoff wavelength in the infrared region. Hence, in this study, a method to mitigate the effect of the InGaAs/Si lattice mismatch on APD performance from the source side is theoretically proposed. Here, a -Ge or poly -Ge bond layers are introduced into the InGaAs/Si bond interface, and the variation in the InGaAs/Si APD performance with the bond layer thickness is simulated and compared. In this work, theoretical guidance for the development of ultralownoise and highgain InGaAs/Si APDs will emerge.Methods An a -Ge or poly -Ge bond layer is introduced into the InGaAs/Si bond interface, and variations in APD performance with bond layer thickness are simulated and compared. Initially, the optical and dark currents of the APD are simulated and compared considering the thickness of the bonding layer. Subsequently, the recombination rate and carrier concentration of the APD under light conditions are simulated to understand the cause of the change in the APD optical current. To further understand the cause of the change in the electron concentration of the APD, the changes in the APD energy band under light conditions are simulated. Then, the changes in charge concentration, impact ionization rate, electric field, and other parameters with the bond layer thickness are simulated and compared. Finally, the gain and gain bandwidth products of the APD are simulated and compared to further explore the performance improvement of the device.
Results and DiscussionsAfter introducing a -Ge or poly -Ge bond layers, the dark current of the APD before avalanche can be as low as 10 -11 A (Fig. 2). Moreover, potential barriers or wells appear in the energy band of the bonding interface (Figs. 8 and 9).Owing to the barrier effect and hole trapping effect, optical and dark current gaps appear in both (Fig. 2), and this phenomenon is more obvious in the APD with the poly -Ge bond layer. These results indicate that both the a -Ge and poly -Ge bonding layers can reduce device noise. The gain and gainbandwidth products of the APD are simulated and compared. The results show that when a -Ge is used as the bonding layer and the thickness of the bonding layer is 0.5 nm, the gain and gain bandwidth product can reach its maximum. The maximum gain of the ...
