Portland State University. Department of Electrical and Computer Engineering
Date of Award
Master of Science (M.S.) in Electrical and Computer Engineering
Electrical and Computer Engineering
1 online resource (viii, 49 pages)
Over the last 5 decades, the semiconductor industry has been well served by Si based technology due to its abundant availability, lower manufacturing cost, large wafer sizes and less complexity in fabrication. Over this period, electronic devices and integrated systems have been miniaturized by downscaling of the transistors. The miniaturization has been guided by the Moore's law where the numbers of transistors have doubled over every two years. However, the trend of transistor miniaturization is fast approaching its limit. Hence, alternate and innovative solutions are necessary to tackle this problem and this propels the research for finding novel materials with unique properties.
The isolation of graphene, a single layer of graphite in 2004 had dramatically pioneered a new regime of research and investigation as a potential material to replace traditional Si. Graphene is the most widely studied two dimensional (2D) material exhibiting fascinating electronic, optoelectronic and electrochemical properties. Room temperature graphene has very high carrier mobility, a hundred times larger than that of Si, but it lacks a bandgap preventing its application in digital electronics. However, the advent of graphene initiated exploration of other 2D materials as a possible replacement for Si for future generation of electronic devices. Other 2D layered materials include transition metal dichalcogenides (TMDs), other layered metal chalcogenides, black phosphorus (BP), boron nitride (BN) etc which are also attractive due to fascinating electronic band structure and layer dependent properties that have demonstrated potential applications in optoelectronics and semiconductor devices. Metal chalcogenides are among the well-studied layered materials that have been isolated as high-quality and two-dimensional crystals. Among the 2D layered metal chalcogenide materials is tin selenide (SnSe), which belongs to group IV--VI that has attracted considerable attention due to its interesting structural and optical properties, hence it has potential applications in optoelectronics, photovoltaics, memory, energy storage, and catalysis.
To date, SnSe films have been produced by exfoliation or chemical vapor deposition that produces flaky films. In this research, uniform, smooth and high quality SnSe thin films were grown over large area (5cm x 5cm) Si/SiO2 substrates using Atomic Layer Deposition (ALD). Films were grown over a temperature range of 350°C to 450°C, which exhibit p- type semiconductor characteristics. ALD is perfect for the growth of layered materials due to its precise controllability of film composition and thickness as the growth proceeds layer by layer. Structural and optical properties of the as-grown films were investigated using X-ray diffraction (XRD), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). These analyses show growth of 2 dimensional, orthorhombic phase films. Magnetic analysis shows a paramagnetic behavior. Back-gated transistors were fabricated for electrical characterization which showed p-type conductance, with an average hole mobility of 10 cm2/V.s and Ion/Ioff ratio of ~105.
Afrin, Shakila, "Investigation of Electronic and Optical Properties of 2-Dimensional Semiconductor Tin Selenide (SnSe) Thin Films" (2019). Dissertations and Theses. Paper 4862.