Browsing by Subject "Field-effect transistors"
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Item Device physics and charge transport of field-effect transistors based on advanced organic semiconductors and graphene(2012-12) Ha, Tae-Jun; Dodabalapur, Ananth, 1963-; Neikirk, Dean P; Bank, Seth; Akinwande, Deji; Nadkarni, SuvidThis dissertation consists of six chapters: In the first chapter, electrical and material properties and charge transport in organic semiconductors and graphene based field-effect transistors (FETs) are introduced. In the second chapter, device architectures of indenofluorene-phenanthrene copolymer based thin-film transistors (TFTs) are discussed. The combination of recessed source/drain and surface treatments on electrical contact and low-voltage-operated TFTs with solution-processed high-k dielectric are investigated. In the third chapter, device physics and charge transport of diketopyrrolopyrrole-naphthalene copolymer based TFTs are discussed. Top-gate TFTs with the polymer dielectric exhibit mobilities of ~1 cm2/V-s and charge transport measurements in steady-state and under non-quasi-static conditions reveal device physics in dual-gate configuration. In the fourth chapter, device characteristics and charge transport in ambipolar diketopyrrolopyrrole-benzothiadiazole copolymer based TFTs are focused. The ambipolar polymer TFTs possess balanced electron and hole mobilities which are both > 0.5 cm2/V-s. The trap density of states is calculated using two analytical methods developed by Lang et al. and Kalb and Batlogg. In the fifth chapter, charge transport of diketopyrrolopyrrole-thiophene copolymer based TFTs employing 4-point-probe configuration is studied. Such polymer TFTs possess the mobilities of up to 3 cm2/V-s. The activation energy as a function of carrier concentration represents multiple trapping and thermally release model or Monroe-type model of charge transport. In the sixth chapter, transformation of electrical characteristics of graphene FETs with an interacting capping layer of fluoropolymers and pi-conjugated organic semiconductors is investigated. The electrical properties of graphene by wafer-scale chemical vapor deposition can be favorably tuned by fluorocarbon capping methods.Item In-situ chemical doping of silicon nanowires by supercritical-fluid synthesis(2016-05) Villarreal, Julián Enrique; Korgel, Brian Allan, 1969-; Koo, Joseph; Paul, Donald R; Shih, Chih-KangSilicon nanowires show promise as components in electronic devices and integrated circuits. The ability to chemically dope nanowires is desirable in order to enable further technological development of this material. In this study, phosphorus-doped (P-doped) silicon nanowires were synthesized in situ by the supercritical fluid-liquid-solid (SFLS) growth mechanism through addition of diphenylphosphine (DPP) or tris(trimethylsilyl)phosphine (P(SiMe3)3) as phosphorus dopants. Conduction electrons from P donor states in crystalline Si have been observed in the in-situ-doped nanowires by detection of a resonance peak at g = 1.998 via electron paramagnetic resonance spectroscopy (EPR) at 4.2 K. Elemental analysis via inductively coupled plasma-atomic emission spectroscopy (ICP-AES) has shown that the amount of P in in-situ-doped nanowires is commensurate with the dose of P precursor, and by appropriate dosing, the doping level can be modulated between 10^17 and 10^19 P atoms cm^−3 without an intolerable degradation in nanowire quality or yield. Field-effect transistors (FETs) were fabricated from the undoped and doped nanowires. An n-channel, field-effect response was in general not clearly observed in FETs fabricated using the in-situ-doped nanowires, though in some cases unipolar p-type and ambipolar behavior were observed with strong hysteresis regardless of the direction of the gate-voltage sweep. The poor performance of the tested devices might be attributed to the use of Au seeds, which introduce mid-gap trap states in Si, and to the presence of surface defects that can scatter charge carriers. In addition, ion implantation of silicon nanowires was performed, as an alternative to in-situ doping of P. The nanowires were subjected to ion implantation at targeted dopant concentrations similar to those of in-situ doping. FET transfer characteristics of these implantated nanowires were determined for as-received nanowires as well as post-implantation annealed nanowires. FET characterization was inconclusive, and EPR studies did not reveal a clear sign of conduction electrons from P. However, compelling changes in the surface states of the nanowires were revealed. In particular, for annealed nanowires, paramagnetic states associated with oxide defects in silicon were observed. Nevertheless, high-resolution transmission electron microscopy did not reveal widespread amorphization of silicon nanowires after ion implantation, as might be expected in bulk silicon. These results suggest that ion implantation of silicon nanowires has a strong effect on surface states, while leaving the crystalline core of the nanowires relatively intact.Item Reliability of a Gallium Arsenide MESFET(Texas Tech University, 1980-12) Yin, Chenwei JohnNot Available.Item Reliability study of gallium arsenide refractory gate field effect transistors(Texas Tech University, 1983-12) Kafati, Eduardo KNot availableItem Submicron and nanoscale organic field-effect transistors and circuits(2006) Jung, Tae Ho; Dodabalapur, Ananth, 1963-Item The analysis of the steady-state thermal and electrical behavior of a silicon metal-oxide-semiconductor field effect transistor.(Texas Tech University, 1975-08) Akers, Lex A..Item The investigation of MOSFET transistors at low temperature(Texas Tech University, 1980-12) Fang, Bo-shungNot available