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High Electron Mobility Thin ‐ Film Transistors Based on Solution ‐ Processed Semiconducting Metal Oxide Heterojunctions and Quasi ‐ Superlattices

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ABSTRACT

High mobility thin‐film transistor technologies that can be implemented using simple and inexpensive fabrication methods are in great demand because of their applicability in a wide range of emerging optoelectronics. Here, a novel concept of thin‐film transistors is reported that exploits the enhanced electron transport properties of low‐dimensional polycrystalline heterojunctions and quasi‐superlattices (QSLs) consisting of alternating layers of In2O3, Ga2O3, and ZnO grown by sequential spin casting of different precursors in air at low temperatures (180–200 °C). Optimized prototype QSL transistors exhibit band‐like transport with electron mobilities approximately a tenfold greater (25–45 cm2 V−1 s−1) than single oxide devices (typically 2–5 cm2 V−1 s−1). Based on temperature‐dependent electron transport and capacitance‐voltage measurements, it is argued that the enhanced performance arises from the presence of quasi 2D electron gas‐like systems formed at the carefully engineered oxide heterointerfaces. The QSL transistor concept proposed here can in principle extend to a range of other oxide material systems and deposition methods (sputtering, atomic layer deposition, spray pyrolysis, roll‐to‐roll, etc.) and can be seen as an extremely promising technology for application in next‐generation large area optoelectronics such as ultrahigh definition optical displays and large‐area microelectronics where high performance is a key requirement.

No MeSH data available.


Energy levels of the metal oxide semiconductors. a) Measured energy levels of the individual oxides used in QSL‐I before contact. b) Schematic energy band diagram of QSL‐I after contact. c) Energy levels of the individual oxides used in QSL‐III before contact. d) Schematic energy band diagram of QSL‐III after contact. The energy bandgaps, Fermi energy levels, and valence band maximum (VBM) energy for each oxide material were determined using UV–vis absorption, KP and UPS measurements, respectively (see Figures S4–S6, Supporting Information).
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advs201500058-fig-0004: Energy levels of the metal oxide semiconductors. a) Measured energy levels of the individual oxides used in QSL‐I before contact. b) Schematic energy band diagram of QSL‐I after contact. c) Energy levels of the individual oxides used in QSL‐III before contact. d) Schematic energy band diagram of QSL‐III after contact. The energy bandgaps, Fermi energy levels, and valence band maximum (VBM) energy for each oxide material were determined using UV–vis absorption, KP and UPS measurements, respectively (see Figures S4–S6, Supporting Information).

Mentions: Figure4a displays the measured energy levels of the individual oxide layers used to form the heterojunction and QSL‐I, before contact. In contrast to previously published studies in which bi‐layered metal oxide structures and transistor channels were formed using similar chemical elements,48, 49 in the present systems, the large difference in the Fermi energies (ΔEF) between the ZnO and In2O3 layers (≈300 meV) is expected to lead to electron transfer from ZnO to In2O3 upon physical contact (Figure 4b). Since the available energy levels at the CBM in the ultrathin In2O3 are quantized (Figure 2c), the transferred electrons may well be confined in a 2D potential well. On the basis of this discussion, it is not unreasonable to assume that the confined electrons will resemble the 2DEG system formed in the MgZnO/ZnO heterointerface.19 However, due to the polycrystalline nature of the In2O3 layer (Figure 1f), the confined electrons are not expected to behave like classic 2DEGs since macroscopic conduction in the QSL‐I is expected to be hindered by the presence of grain boundaries that are clearly visible in the high‐resolution transmission electron microscope (HRTEM) images in Figure 1.


High Electron Mobility Thin ‐ Film Transistors Based on Solution ‐ Processed Semiconducting Metal Oxide Heterojunctions and Quasi ‐ Superlattices
Energy levels of the metal oxide semiconductors. a) Measured energy levels of the individual oxides used in QSL‐I before contact. b) Schematic energy band diagram of QSL‐I after contact. c) Energy levels of the individual oxides used in QSL‐III before contact. d) Schematic energy band diagram of QSL‐III after contact. The energy bandgaps, Fermi energy levels, and valence band maximum (VBM) energy for each oxide material were determined using UV–vis absorption, KP and UPS measurements, respectively (see Figures S4–S6, Supporting Information).
© Copyright Policy - creativeCommonsBy
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC5016782&req=5

advs201500058-fig-0004: Energy levels of the metal oxide semiconductors. a) Measured energy levels of the individual oxides used in QSL‐I before contact. b) Schematic energy band diagram of QSL‐I after contact. c) Energy levels of the individual oxides used in QSL‐III before contact. d) Schematic energy band diagram of QSL‐III after contact. The energy bandgaps, Fermi energy levels, and valence band maximum (VBM) energy for each oxide material were determined using UV–vis absorption, KP and UPS measurements, respectively (see Figures S4–S6, Supporting Information).
Mentions: Figure4a displays the measured energy levels of the individual oxide layers used to form the heterojunction and QSL‐I, before contact. In contrast to previously published studies in which bi‐layered metal oxide structures and transistor channels were formed using similar chemical elements,48, 49 in the present systems, the large difference in the Fermi energies (ΔEF) between the ZnO and In2O3 layers (≈300 meV) is expected to lead to electron transfer from ZnO to In2O3 upon physical contact (Figure 4b). Since the available energy levels at the CBM in the ultrathin In2O3 are quantized (Figure 2c), the transferred electrons may well be confined in a 2D potential well. On the basis of this discussion, it is not unreasonable to assume that the confined electrons will resemble the 2DEG system formed in the MgZnO/ZnO heterointerface.19 However, due to the polycrystalline nature of the In2O3 layer (Figure 1f), the confined electrons are not expected to behave like classic 2DEGs since macroscopic conduction in the QSL‐I is expected to be hindered by the presence of grain boundaries that are clearly visible in the high‐resolution transmission electron microscope (HRTEM) images in Figure 1.

View Article: PubMed Central - PubMed

ABSTRACT

High mobility thin‐film transistor technologies that can be implemented using simple and inexpensive fabrication methods are in great demand because of their applicability in a wide range of emerging optoelectronics. Here, a novel concept of thin‐film transistors is reported that exploits the enhanced electron transport properties of low‐dimensional polycrystalline heterojunctions and quasi‐superlattices (QSLs) consisting of alternating layers of In2O3, Ga2O3, and ZnO grown by sequential spin casting of different precursors in air at low temperatures (180–200 °C). Optimized prototype QSL transistors exhibit band‐like transport with electron mobilities approximately a tenfold greater (25–45 cm2 V−1 s−1) than single oxide devices (typically 2–5 cm2 V−1 s−1). Based on temperature‐dependent electron transport and capacitance‐voltage measurements, it is argued that the enhanced performance arises from the presence of quasi 2D electron gas‐like systems formed at the carefully engineered oxide heterointerfaces. The QSL transistor concept proposed here can in principle extend to a range of other oxide material systems and deposition methods (sputtering, atomic layer deposition, spray pyrolysis, roll‐to‐roll, etc.) and can be seen as an extremely promising technology for application in next‐generation large area optoelectronics such as ultrahigh definition optical displays and large‐area microelectronics where high performance is a key requirement.

No MeSH data available.