In this study, we propose the fabrication of a photodetector based on the heterostructure of p-type Si and n-type MoS 2 . Mechanically exfoliated MoS 2 flakes are transferred onto a Si layer; the resulting Si−MoS 2 p−n photodiode shows excellent performance with a responsivity (R) and detectivity (D*) of 76.1 A/ W and 10 12 Jones, respectively. In addition, the effect of the thickness of the depletion layer of the Si−MoS 2 heterojunction on performance is investigated using the depletion layer model; based on the obtained results, we optimize the photoresponse of the device by varying the MoS 2 thickness. Furthermore, low-frequency noise measurement is performed for the fabricated devices. The optimized device shows a low noise equivalent power (NEP) of 7.82 × 10 −15 W Hz −1/2 . Therefore, our proposed device could be utilized for various optoelectronic devices for low-light detection.

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A physical unclonable function (PUF) device using a nano-electromechanical (NEM) switch was demonstrated. The most important feature of the NEM-switch-based PUF is its use of stiction. Stiction is one of the chronic problems associated with micro- and nano-electromechanical system (MEMS/NEMS) devices; however, here, it was utilized to intentionally implement a PUF for hardware-based security. The stiction is caused by capillary and van der Waals forces, producing strong adhesion, which can be utilized to design a highly robust and stable PUF. The probability that stiction will occur on either of two gates in the NEM switch is the same, and consequently, the occurrence of the stiction is random and unique, which is critical to its PUF performance. This uniqueness was evaluated by measuring the interchip Hamming distance (interchip HD), which characterizes how different responses are made when the same challenge is applied. Uniformity was also evaluated by the proportion of "1" or "0" in the response bit-string. The reliability of the proposed PUF device was assessed by stress tests under harsh environments such as high temperature, high dose radiation, and microwaves.

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