Size-Dependent Photoresponse of Germanium Nanocrystals-Metal Oxide Semiconductor Photodetector

In this article, size-dependent photoresponse characteristics and low-frequency noise behavior of high-speed germanium nanocrystals (nc-Ge) photodetector have been reported. The nc-Ge embedded in SiO
₂
matrix with different sizes have been synthesized by annealing the cosputtered Ge-SiO
₂
thin films at 800 °C-900 °C. It has been observed that the photoresponse of the detector increases with the increasing size of nc-Ge. The sample annealed at 900 °C showed maximum responsivity (3.5 A/W) with the fast response time. The low-frequency noise spectral power density in the current fluctuation (S
_I
) have been measured for the fabricated nc-Ge photodetectors, and lowest noise equivalent power (NEP) and highest detectivity (D*) have been observed in the nc-Ge detector synthesized at 900 °C. Tunable responsivity in nc-Ge has been observed due to size-dependent light absorption, electric field-driven carrier separation, and tunneling through the oxide barriers. The transient photoresponse behavior has also been studied and the best rise time of 6.2 μs was observed for nc-Ge synthesized at 900 °C. These results suggest that the nc-Ge are a promising contender for high-performance integrated optoelectronic devices that are fully compatible with silicon technology in terms of fabrication and thermal budget.