Fabrication and Characterization of Optoelectronics Non-volatile Memory Devices based on 2D Materials

Student thesis: Master's Thesis


The development of digital technology permits the storage and processing of binary data at high rates, with high precision and density. Therefore, over the past few decades, Moore's law has pushed the development of scaling semiconductor devices for computing hardware. Although the current downward scaling trend has reached its scaling limits, a new "More-than-Moore" (MtM) trend has been emphasized as a diversified function of data collection, storage units, and processing devices. The function diversification defined in MtM can be viewed as an alternative form of "scaling down" for electronic systems, as it incorporates non-computing functions into digital ones, allowing digital devices to interact directly with the environment around them. Two-dimensional (2D) materials display promising potential for combining optical sensing and data storage with broadband photoresponse, outstanding photoresponsivity, rapid switching speed, multi-bit data storage, and high energy efficiency. In this work, in-solution 2D materials flakes (Hafnium Diselenide (HfSe2) and Germanium Selenide (GeSe) have been studied as a charge-trapping layer in non-volatile memory through the seamless fabrication process. Furthermore, the behavior of fabricated non-volatile memories under light illumination has been investigated towards in-memory light sensing. Atomic Force Microscopy, RAMAN spectroscopy, and X-ray Diffraction Spectroscopy characterized the charge-trapping materials. The electrical characterization of Metal Oxide Semiconductor (MOS) Capacitor memory revealed a memory window of 4V for the HfSe2 device under ±10V biasing. Intriguingly, the GeSe device exhibited an extraordinarily wide memory window of 11V under the same electrical biasing. Furthermore, the memory endurance for both materials as charge trapping layer (CTL) exceeds the standard threshold of electrical programming and erasing cycles. The accelerated retention test at different temperatures showed the memory device's stability and reliability for both materials. Under light stimuli with electrical readout voltage, the MOS memory exhibited wavelength and intensity-responsive behavior. The MOS memory of HfSe2 has demonstrated remarkable capabilities in storing the detected light signal, while also exhibiting a noteworthy increase in the memory window of approximately 1.8 V when subjected to a laser wavelength of 405 nm. Meanwhile, the GeSe device's CV measurement revealed a similar trend with the greatest memory window enhancements occurring in relation to 465 nm laser wavelength. Under ±6 V biasing in the absence of light, the memory window was found to be 8.3 V. However, following exposure to a 465 nm laser, this value increased significantly to 9.9 V, representing an increment of 1.6 V. In addition, both devices exhibited distinct sensing of various light intensities and an enhanced memory window as a result of the observable Vt shift caused by altering the levels of illumination. This memory enhancement suggests that photoexcited carriers in the CTL layer were responsible for the optical memory behavior. The 2D materials as CTL pave the way for a reconfigurable optical memory with multilevel optical data storage capacity. This research represents a significant step towards the development of a new generation of memory devices that can store and retrieve data using light signals.
Date of AwardJul 2023
Original languageEnglish (US)
Awarding Institution
  • Computer, Electrical and Mathematical Sciences and Engineering
SupervisorNazek Elatab (Supervisor)


  • Optoelectronic
  • Memory
  • Nonvolatile
  • 2D Materials
  • Tow Dimensional
  • HfSe2
  • GeSe
  • Hafnium Diselenide
  • Germanium Selenide
  • charge-trapping Memory

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