Some of the material in is restricted to members of the community. By logging in, you may be able to gain additional access to certain collections or items. If you have questions about access or logging in, please use the form on the Contact Page.
Garcia, C. G. (2021). Optical and Electro-Optical Properties of Two-Dimensional Semiconductors. Retrieved from https://purl.lib.fsu.edu/diginole/2020_Summer_Fall_Garcia_fsu_0071E_16439
Two-dimensional (2D) materials have recently caught much attention due to their exceptional properties and their potential applications in opto-electronics. Graphene, transition metal dichalcogenides (TMDs), and black phosphorus (b-P) are some of the main candidates from the 2D material family that show great promise in their ability to have properties such as high mobility, anisotropy, desirable band gap, and many more. Here, we'll discuss some of the history of these 2D semiconductors and some of the properties that make them unique and interesting. This will be focusing on the electrical and opto-electrical properties of 2D semiconductors in measurements conducted during my graduate research studies. Some of these measurements include 2-terminal and 4-terminal contact configurations, photoconductivity, transport, photoluminescence, and Raman spectroscopy. The 2D semiconductors used in these experiments are post-graphene such as TMDs, post transition metals, and b-P. The photoconductivity was measured on few-layered WSe$_{2}$ field-effect transistors (FETs) using both 2-terminal and 4-terminal configurations under 532~nm laser source. For an incident laser power of 248 nW, we extracted 18 A/W and $\sim$4000\% for the two-terminal responsivity (R) and an external quantum efficiency (EQE) respectively, when a bias voltage $V_{ds}$ = 1 V and a gate voltage $V_{bg}$ = 10 V were applied to the sample. R and EQE saw an increase by 370\% to $\sim$85 A/W and $\sim$20000\% respectively, when using a four-terminal configuration. The photogating effect was observed in our few-layered (3–4 layers) ReS$_{2}$ FETs in which varying the incident optical power shifted the FETs’ threshold voltage. The photogating effect produced a significant gain in the electrical response of the FETs to incident light as measured by R and EQE. We obtained a maximum R of 45 A/W corresponding to an EQE of $\sim$10500\% in a 4-terminal measurement of the photoconductivity in the ON-state. We attribute both the photogating and the observed gain to the influence of charge traps. We also presented a detailed study on the Raman spectra and on the temperature dependence of the electrical transport properties of arsenic-doped black phosphorus (b-AsP) with an As fraction of x = 0.25. Field-effect transistors fabricated from few-layered b-AsP exfoliated onto Si/SiO$_{2}$ substrates exhibited hole-doped like conduction with a room temperature ON/OFF current ratio of $\sim$10$^{3}$ and an intrinsic field-effect mobility approaching $\sim$300 cm$^{2}$V$^{-1}$s$^{-1}$ at 300 K which increases up to 600 cm$^{2}$V$^{-1}$s$^{-1}$ at 100 K when measured via a 4-terminal method. The ON to OFF current ratio is observed to increase up to 10$^{5}$ at 4 K. Similarly to pristine b-P, its transport properties revealed a high anisotropy between armchair and zig-zag directions. Photoluminescence (PL) and transport measurements were conducted on vanadium-doped InSe FETs using 2-terminal configuration under 532 nm and 785 nm excitation. Low temperature measurements were also studied ranging from 295 K to $\sim$13 K in a cryostat. Transport measurements showed little to no current when drain-source and back-gate voltages were applied and under low temperature. Low temperature PL showed blue-shifted peaks at T $>$ 50 K and red-shifted peaks at T $<$ 50 K. Lastly, there are summaries on papers that I had a smaller role.
A Dissertation submitted to the Department of Physics in partial fulfillment of the requirements for the degree of Doctor of Philosophy.
Bibliography Note
Includes bibliographical references.
Advisory Committee
Stephen McGill, Professor Co-Directing Dissertation; Efstratios Manousakis, Professor Co-Directing Dissertation; Geoffrey Strouse, University Representative; Irinel Chiorescu, Committee Member; David Collins, Committee Member.
Publisher
Florida State University
Identifier
2020_Summer_Fall_Garcia_fsu_0071E_16439
Garcia, C. G. (2021). Optical and Electro-Optical Properties of Two-Dimensional Semiconductors. Retrieved from https://purl.lib.fsu.edu/diginole/2020_Summer_Fall_Garcia_fsu_0071E_16439