"Femtosecond laser hyperdoped silicon, also known as the black silicon (BS), has a large number of defects and damages, which results in unstable and undesirable optical and electronic properties in photonics platform and optoelectronic integrated circuits (OEICs). We propose a novel method that elevates the substrate temperature during the femtosecond laser irradiation and fabricates tellurium (Te) hyperdoped BS photodiodes with high responsivity and low dark current. At 700 K, uniform microstructures with single crystalline were formed in the hyperdoped layer. The velocity of cooling and resolidification is considered as an important role in the formation of a high-quality crystal after irradiation by the femtosecond laser. Because of the high crystallinity and the Te hyperdoping, a photodiode made from BS processed at 700 K has a maximum responsivity of 120.6 A/W at 1120 nm, which is far beyond the previously reported Te-doped silicon photodetectors. In particular, the responsivity of the BS photodiode at 1300 nm and 1550 nm is 43.9 mA/W and 56.8 mA/W with low noise, respectively, which is valuable for optical communication and interconnection. Our result proves that hyperdoping at a high substrate temperature has great potential for femtosecond-laser-induced semiconductor modification, especially for the fabrication of photodetectors in the silicon-based photonic integration circuits."
Can someone explain to me what the process behind the high responsivity in the near infrared is? My calculation says it is 13 300 % quantum efficiency (133 electrons/photon) at 1120 nm. Have they made an avalanche photo diode with 2 V bias?
ReplyDeleteIn my point of view we are talking here more of a photoconductor than a photodiode, or both of them in parallel. The reverse dark characteristic is not much different from the forward. The curves log-shaped curve in a log/lin chart look much like a linear = resistive response.
ReplyDeleteCertainly a true pn diode cannot have gain, except in the case of avalanche gain. This structure appears to be Te dopes silicon on n-type silicon substrate, which would possibly be a n++/n- structure, which is not a pn diode. So this device more closely represents a Schottky photodiode, which also cannot have gain. Most likely, there is trap filling that lowers the Schottky barrier height, causing a change in the leakage current, which looks like gain, but is pretty useless for most applications.
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