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

Abstract

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 SiO2 matrix with different sizes have been synthesized by annealing the cosputtered Ge-SiO2 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 ( ${S}_{\text {I}}$ ) have been measured for the fabricated nc-Ge photodetectors, and lowest noise equivalent power (NEP) and highest detectivity ( ${D} ^\ast $ ) 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 $6.2~\mu \text{s}$ 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.