Extension of spectral sensitivity of GeSn IR photodiode after laser annealing

Highlights: • Laser annealing was applied for Sn redistribution in GeSn material. • Infrared photodiodes with enhanced sensitivity in infrared were formed. • Fast photodiode response was characterized for suitability in image sensors. Photo-detection in the near-infrared is commonly performed by Ge or InGaAs-based photodetectors. Further extension of the detection range to the mid-infrared region can be performed by germanium-tin (GeSn) material which shows promising characteristics and is fully compatible with silicon electronics as can be directly grown on silicon substrates. In this study, we focused on the optoelectronic properties of the photodiodes prepared by using 200 nm thick Ge_0.95Sn_0.05 epitaxial layers on Ge/n-Si substrate with aluminium contacts. Photodiodes were formed on non-irradiated and Nd:YAG laser irradiated Ge_0.95Sn_0.05 layers. The samples were irradiated by pulsed Nd:YAG laser with 61.5–259.2 MW/cm² intensity. The photodiodes were characterized by using short laser pulses with the wavelength in 2.0–2.6 μm range. The laser-irradiated diode was found more sensitive in the long wavelength range due to laser induced Sn atoms redistribution providing formation of graded bandgap structure. Sub-millisecond photocurrent relaxation in the diodes revealed their suitability for image sensors. Our findings open the perspective for improving the photo-sensitivity of GeSn alloys in the mid-infrared by pulsed laser processing.