Effect of bubbles at the bonded interface on the performance of GeSn/Si PIN photodetector

Abstract

Due to the large lattice mismatch between GeSn and Si materials, high-density threading dislocation (TD) forms when GeSn films are grown by epitaxial growth. This leads to the increase of the dark current density (DCD) of the device. The wafer-bonded technique is a promising method to prepare high-quality thin films. This has been used to produce the Si-based GeSn materials with low TDD. However, there are a lot of bubbles at the bonded interface, resulting in the deterioration of the performance of the device. The study of bubbles on the performance of the GeSn PIN photodetector (PD) has not been reported. In this paper, the effects of the bonding bubbles on the performance of the device are performed. The photocurrent, dark current, charge concentration, electric field, and 3dB-bandwidth (BW) as a function of the bubble radius and thickness are demonstrated. The effects of the bubble radius and thickness on the 3dB-BW (∼18 GHz) are insignificant when the bubble thickness and radius are set as 1 nm and 1 μm, respectively. The 3dB-BW decreases to ∼17 GHz when the bubbles are close to the sizes of the top mesa. However, the 3dB-BW drops drastically with the increase of the bubble thickness when the bubble radius reaches 7 μm. Most importantly, the 3dB-BW sharply decreases to ∼30 MHz regardless of the thickness of the bubble when the bubble radius of 14 μm is set. This may provide guidance for the application of the wafer-bonded GeSn PIN PD.