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Title: Low-temperature solution-processed metal oxide semiconductors for large-area electronics
Author: Das, Satyajit
ISNI:       0000 0004 9350 9067
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2019
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In recent years, solution-processed metal oxide semiconductor thin-film transistors (TFTs) have shown great promise as an emerging technology in the field of large-area electronics. This has been possible due to a range of favourable properties, such as high charge carrier mobility, low power consumption, optical transparency and mechanical flexibility. However, emerging electronic applications such as high-definition displays demand TFTs with ever increasing performance characteristics that are inaccessible by existing technologies. This thesis focuses on developing TFTs based on metal oxides beyond the current state-of-the-art performance via low-temperature (<250°C), solution-processed methods and the compatibility of these devices on temperature sensitive and inexpensive flexible plastic substrates. The work first explores low-dimensional high performance ultra-thin (<15 nm) In2O3/ZnO heterojunction (HJ) TFTs, in which the In2O3 and ZnO layers were deposited via ultrasonic spray pyrolysis (SP) in ambient conditions and spin coating, respectively. Using this bi-layer approach, the impact of the second semiconducting layer on the electrical performance and on the interface(s) was studied using different characterisation methods. The results demonstrated TFTs with enhanced electron mobilities of 40 – 50 cm2/Vs. The next part of this work explores a facile n-type doping approach of the HJ TFTs described in the previous part. An additional layer of fullerenes (pristine and doped) was introduced on top of the oxide bi-layers to study the concept of hybrid modulation doping (MOD) in organic-metal oxide layered semiconductors. Using electrical and optical characterisations, the effect of this extra doping layer was evaluated on the HJ TFT performance. The third part discusses the utilisation of high-κ oxides (ZrO2, Y2O3 and ZrO2:Y2O3 blend) dielectric system for high-performance In2O3/ZnO HJ TFTs on inexpensive flexible polyimide (PI) substrates, where all layers were deposited via spin coating. Using these dielectrics, TFTs with electron mobilities 15 – 25 cm2/Vs and a reduced operating voltage (± 2V) were observed. The final part introduces the concept of hybrid perovskite-oxide phototransistors, where CH3NH3PbI3 perovskite nanocrystals (NCs) were deposited on top of two different bi-layer TFTs (In2O3/ZnO and In2O3/Al-ZnO) to study their light response. The transistors were exposed to light at different wavelengths and the results demonstrate a high photoresponse at shorter wavelengths, i.e. near UV region with maximum responsitivity of around 104 (A/W), which is at least a few orders of magnitude higher than previously reported values for metal-oxide based phototransistors.
Supervisor: Anthopoulos, Thomas ; McLachlan, Martyn Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral