Infrared detectivity in p-GeSn/n-Ge junction for multispectral sensing

This study investigates the dominant noise source in Ge_0.93Sn_0.07/Ge PN junction photodetector to enhance its performance for multispectral infrared sensing. A 50-nm-thick p-type Ge_0.93Sn_0.07 film was grown on an n-Ge substrate by molecular beam epitaxy to form a mesa-structured photodiode. To identify the dominant noise mechanisms, the current noise power density spectrum was analyzed over a frequency range from 1 to 200 Hz at various operating temperatures. The results reveal that, at room temperature, generation-recombination (GR) noise dominates within the typical operating frequency range of 10–100 Hz. In contrast, at a reduced temperature of 240 K, the noise spectrum becomes flat above 10 Hz and agrees well with the calculated thermal noise. These findings indicate that suppressing GR noise is critical for improving detectivity at room temperature, while reducing leakage current, likely associated with mesa sidewalls, is essential for enhancing detector performance during cooled operation.