Browsing by Subject "SrSnO3"

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    Exploration of Carrier Transport and Novel Devices in Emerging Semiconductors
    (2022-08) Golani, Prafful
    With scaling and performance of silicon-based transistors reaching their fundamental limits, a cross-disciplinary effort has gone into identification of novel material systems and device architectures that can outperform conventional solutions. Two systems that have shown good promise are van der Waals (vdW) semiconductors and semiconducting perovskite oxides. vdW semiconductors have already been used to demonstrate conventional MOSFETs and TFETs because of their atomically smooth surfaces and extremely thin body thicknesses which result in enhanced electrostatic gate control and improved scalability. On the other hand, semiconducting perovskite oxides have a large bandgap, low carrier effective masses and ability to form unique heterostructures making them interesting candidates for high-power high-frequency applications. The purpose of this thesis is to explore the electrical and material characterization results of electronic devices fabricated from Black Arsenic (vdW semiconductor) and SrSnO3 (perovskite oxide), by diving into their fundamental carrier transport studies. Exfoliated flakes of black arsenic (BAs) were used to fabricate MOSFETs which demonstrated ambipolar transport. The fabricated devices showed layer-dependent transport with high on/off ratios, high mobility and low off-current. Low temperature characterization revealed presence of low Schottky barrier height at the Ni/BAs interface while electron (hole) mobility vs temperature plot showed mobility was phonon limited. To show practical applications, ambipolarity of the devices was used to demonstrate an inverter and a frequency doubler as well. Ni/BAs interface was further explored, which revealed formation of an in-plane metallic contact to the semiconducting channel. Based upon this observation a self-aligned FET with lowered contact resistance is also proposed. Doped SrSnO3 had already been used to demonstrate MESFETs and RF FETs. However, SrSnO3 has low thermal conductivity which can result in degraded performance due to self-heating. An all-electrical method based on pulsed I-V characterization was performed to determine the thermal resistance and quantify the rise in channel temperature of two-terminal devices under electrical bias. TCAD simulations were performed to show that the rise in channel temperature was in close agreement with the experimental values. To further explore the carrier transport, electrical breakdown in undoped films was studied and contact optimization to doped SrSnO3 was also performed.
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    Hybrid Molecular Beam Epitaxy Of Strain-Engineered Srsno3 Films And Heterostructures
    (2018-05) Wang, Tianqi
    Recently, perovskite oxides have been experiencing a resurgence of research interest because of their richness in functionalities and tunability by external stimuli. In particular, owning to the combination of high mobility and large band gap, alkaline earth stannate SrSnO3 starts to gain popularity among researchers and industries for transparent conducting and high power electronics. On the other hand, the hybrid molecular beam epitaxy opens up new revenues for self-regulating growth of perovskite oxides by incorporating chemical precursors into their growth approaches. Driven by the demands of optimal electronic properties and investigation of scattering mechanism, SrSnO3 thin film with excellent structural quality grown by molecular beam epitaxy becomes especially desirable. Thereby, the marriage between these two conceives great potential of scientific discovers in the very beginning. However, pioneering a novel growth approach is challenging and requires preparation work at many aspects such as selection of Sn-based chemical precursors, understanding of the strain relaxation related defect formation, and the control over duel valence states of Sn. In the attempt to high mobility SrSnO3 using hybrid molecule beam epitaxy, a record high room-temperature mobility of 55 cm2V-1s-1 was achieved through systematic control of cation stoichiometry. In addition, the correlation between electronic transport and defect associated with non-stoichiometry and dislocations were revealed. It turned out that non-stoichiometry could lead to a crossover from weak to strong localization of electronic carriers in La-doped SrSnO3. In contrast, substrate-induced dislocations can have a strong influence on the electron phase coherence length resulting in two-dimensional to three-dimensional weak localization crossover. With the growth conditions of high performance SrSnO3, structure and properties of coherent stoichiometric SrSnO3 was then further tuned via strain engineering. Meanwhile, synchrotron-based reciprocal space mapping and half-order diffraction were employed to characterize structural distortions. We demonstrated that in SrSnO3 thin films three distinct phases of tetragonal I4/mcm, high-temperature orthorhombic Imma, and room temperature orthorhombic Pnma can be stabilized under compressive, tensile, and nearly zero strain, respectively. Remarkably, stabilization of high symmetry tetragonal phase SrSnO3 corresponded to a shift of the 1st order phase transition shift by over 800 C and gave rise to an enhancement of 300 % in electron mobility at room temperature. Moreover, chemical doping (< 1 %) by La in SrSnO3 was also found to influence phase stabilization and electronic transport possibly related to anti-site defects. In summary, through the development of hybrid molecular beam epitaxy of SrSnO3 superior structural and electronic properties were attained. Also, structure distortions induced by strain engineering and chemical doping were found to dramatically tailor and enhance SrSnO3 properties. The study in SrSnO3 followed and showcased the very strength of perovskite oxide in research value.
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    Strontium Stannate – An Emerging Wide Gap Semiconductor for Field-Effect Transistor Applications
    (2020-06) Chaganti, Venkata Raghava Saran Kumar
    Perovskite oxides are a promising family of materials with the potential for enabling the development of advanced novel electronic device components. However, the lack of an appropriate channel material has hindered the development of game-changing perovskite-based electronic devices. Perovskite stannates are emerging tin-based perovskite oxide semiconductors that have all the requisite material properties for a channel material and are capable of high electron mobilities at unusually high carrier concentrations. Among the perovskite stannates, barium stannate (BSO) has been the most popularly researched material. Strontium stannate (SSO), another interesting perovskite stannate, has been relatively less explored, even though by virtue of its smaller lattice constant, it is more amenable for heterostructure growth than BSO and for eventual integration with other perovskite oxide materials of novel technological interest. SSO also has a wide band gap in the range of 4-5 eV, which makes it particularly well suited to high-power and radio frequency (RF) applications. These properties provided us enough motivation to explore SSO for field-effect transistor (FET) applications. In this dissertation, the demonstration of first-ever SSO-based FETs with record performance for any stannate-based FET is presented. Further, the challenge of producing low resistance ohmic contacts to SSO is addressed through a systematic study, and optimized contacts for use in FETs are demonstrated. Improvement in performance over our previously reported SSO-based FETs is presented by utilizing a bi-layer film structure and RF operation in SSO-based FETs is also reported. This study lays the foundation for the development of future high-performance and novel perovskite devices.