Performance Enhancement of Ge/Si Avalanche Photodetector by Specific Sidewall Passivation Using Remote Oxygen Plasma Treatment

Abstract We report on an obvious performance enhancement of separated absorption charger-layer multiplication (SACM) Ge/Si avalanche photodetector with the sidewalls passivated by low temperature remote oxygen plasma (ROP) treatment. The dangling bonds on the Ge surface can be efficiently passivated by the formation of ideal Ge/GeO2 interface. With ROP passivation, the leakage current of device shows a (3~4)-fold decrease at 300 K, resulting in a dark current (Idark) of 3.5×10-6 A at 90% avalanche voltage (Vbr) and 3.4×10-7 A at punch-through voltage (Vpuhch-through) for the 26-μm-diameter device. At 200 K, more than 10-fold decrease is demonstrated, and the passivation mechanism is revealed. Moreover, a multiplication gain of 94 is obtained under 1550 nm illumination. The device with ROP passivation shows an improved gain bandwidth product (GBP) of 190 GHz. The enhanced high frequency response of the device with ROP passivation can be ascribed to the relief of the retarding effect caused by the interface state on the sidewalls. An opening eye diagram at 28 Gbps without using any trans-impedance amplifier (TIA) is demonstrated, indicating a reliable device transmission performance.