In this these, in order to enhance the n-channel organic field-effect transistor (OFET) performance, amino functionalized self-assembled monolayers (A-SAMs) which consist of amino groups, a well-known n-type dopant candidate, were introduced from the top of OFET surfaces and on the gate oxide surfaces. To obtain better understanding for optimization of OFET performances we attempted to elucidate the mechanism of surface doping and surface modification by A-SAMs. Both the surface doping and surface modification of the gate oxide approaches have individual pros and cons. One needs to take into account the surface energy properties of SAMs and the resulting OSC film structure and pick the most suitable method to introduce the SAM material to the OFET (either doping or oxide modification) in order to obtain optimized device performances. Our study strongly suggests that both surface doping and surface modification of the gate oxide with A-SAMs could enhance other semiconductor-based electronic device performances.:Abstract v
Chapter 1. Introduction 1
Chapter 2. Theoretical Background 7
2.1. Organic Semiconductors (OSCs) 8
2.1.1. Semiconducting properties of organic molecules 8
2.1.2. Charge Transport Mechanism in OSCs 10
2.2. Organic Field-Effect Transistors (OFETs) 18
2.2.1. Operation Principle 18
2.2.2. Device Geometry of OFETs 20
2.2.3. Contacts (metal/semiconductor junction) in OFETs 21
2.2.4. Dielectric material for OFETs 23
2.2.5. Current-Voltage Characteristics of OFETs 25
2.3. Dominant contributors to OFET Performance 32
2.3.1. Molecular structure and Orientation of OSCs 32
2.3.2. Dielectric/OSC Interface 33
2.3.3. OSC/Contact Interface (Contact resistance) 35
2.3.4. Shallow and deep traps 36
2.4. Strategies to improve OFET performance 37
2.4.1. Introducing dopants to OFETs 37
2.4.2. Modification of Gate Oxide Layer with SAMs 44
Chapter 3. Experimental 51
3.1. Device Fabrication 52
3.1.1. Device type I - Substrate/ODTMS/PTCDI-C8/Au 53
3.1.2. Device type II - Substrate/ODTCS/N2200 (PNDI2OD-2T)/Au 53
3.1.3. Device type III - Substrate/SAMs/PTCDI-C8/Au 54
3.2. Surface doping process 56
3.2.1. Surface dopant – Aminosilanes (A-SAMs) 56
3.2.2. Surface doping method 56
3.3. Characterization 59
3.3.1. Material characterization 59
3.3.2. Surface-wetting characterization - Contact angle measurement 61
3.3.3. Micro-structure characterization - Atomic Force Microscopy (AFM) 62
3.3.4. Surface potential characterization – Kelvin Probe Force Microscopy (KPFM) 63
3.3.5. Molecular Structure Characterization - Grazing Incidence Wide Angle X-ray Scattering (GIWAXS) 64
3.3.6. Electrical Characterization - Current-voltage (I-V) measurement 66
Chapter 4. Result and Discussion 69
4.1. Optimization of OFETs based on PTCDI-C8 and N2200 70
4.1.1. PTCDI-C8 OFETs 70
4.1.2. N2200 OFETs 72
4.1.3. Device measurement condition 75
4.2. Investigation of Surface doping mechanism of Aminosilanes 77
4.2.1. Surface doping effect depending on the dopant processing method 77
4.2.2. Surface doping effect for different types of organic semiconductors 80
4.2.3. Surface doping effect for different types of surface dopants 89
4.2.4. Surface doping effect for different OSC grain sizes 92
4.2.5. Surface doping effect for different OSC film thicknesses 103
4.2.6. Molecular structure of the doped films identified by GIWAXS 106
4.2.7. Stability of the surface doped OFETs 107
4.2.8. Summary 111
4.3. Modification of the gate oxide with various self-assembled monolayers 112
4.3.1. The surface property of SAM-treated substrates 112
4.3.2. The relation between the OSC morphology and the field-effect mobility 115
4.3.3. The origin of the threshold voltage shift 126
4.3.4. Memristive effects in PTCDI-C8 devices on ODTMS 133
4.3.5. Summary 137
4.4. Comparison of the surface doping and the modification of the gate dielectric 138
4.4.1. The reliability factor of OFETs 138
4.4.2. The threshold voltages and field-effect mobility of OFETs 141
4.4.3. Density of Interfacial trap sites and SAM induced mobile carriers 143
4.4.4. Summary 144
Chapter 5. Conclusion 145
Bibliography 148
List of Figures 158
List of Tables 166
List of Equations 167
Acknowledgment 168
Erklärung zur Eröffnung des Promotionsverfahrens 169
| Identifer | oai:union.ndltd.org:DRESDEN/oai:qucosa:de:qucosa:35131 |
| Date | 22 August 2019 |
| Creators | Shin, Nara |
| Contributors | Leo, Karl, Mannsfeld, Stefan, Reineke, Sebastian, Technische Universität Dresden |
| Source Sets | Hochschulschriftenserver (HSSS) der SLUB Dresden |
| Language | English |
| Detected Language | English |
| Type | doc-type:doctoralThesis, info:eu-repo/semantics/doctoralThesis, doc-type:Text |
| Rights | info:eu-repo/semantics/openAccess |
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