Crystalline InGaZnO Superlattice Nanowires for High-performance Electronic and Photoelectronics


Student thesis: Doctoral Thesis

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Awarding Institution
Award date10 Aug 2020


One-dimensional (1D) semiconductor nanostructures have attracted great interests in the scientific community for the future nanoelectronic device applications. Among them, 1D metal-oxide nanowires (NWs) are regarded as the ideal material for the application for electronic and optoelectronic devices for their extraordinary chemical and physical properties. Here, amorphous indium–gallium–zinc oxide (a-IGZO) materials have been widely explored for various thin-film transistor (TFT) applications; however, their device performance is still restricted by the intrinsic material issues especially due to their non-crystalline nature. To date, because of this disadvantage a-IGZO, there are many experiences with the aim to fabricate the IGZO NWs with crystalline structure and to investigate its electronic and photoelectronic properties. However, the successfully fabricate the highly crystalline IGZO with high quality still remains a substantial challenge, and there are only few works focus on the synthesis of crystalline IGZO NWs with superlattice structure. While, in these works, the quality of the IGZO NWs is not good enough with a rough surface which will deteriating the property of the NWs. Besides, the quaternary crystalline IGZO NWs with excellent superlattice structure and controlled stoichiometry have not been well studied for their electronic and optoelectronic properties.

In this study, highly crystalline superlattice-structured IGZO nanowires with different Ga concentration are successfully fabricated by enhanced ambient-pressure chemical vapor deposition (CVD). Along the NW axial direction, perfect alternately stacking of InGaO(ZnO)4+ blocks and InO2- layers is observed to form a periodic layered structure. The unique superlattice structure together with the optimal Ga concentration (i.e., 31 at.%) are found to effectively modulate the carrier concentration as well as efficiently suppress the oxygen vacancy formation for the superior NW device performance. In specific, the In1.8Ga1.8Zn2.4O7 NW field-effect transistor exhibit impressive device characteristics with the average electron mobility of ~ 110 cm2·V-1·s-1 and on/off current ratio of ~ 106. Importantly, these NWs can also be integrated into NW parallel arrays for the construction of high-performance TFT devices, in which their performance is comparable to many state-of-the-art IGZO TFTs. All these results can evidently indicate the promising potential of these crystalline superlattice-structured IGZO NWs for the practical utilization in next-generation metal-oxide TFT device technologies.

Furthermore, due to the efficient photocarrier separation and collection coming from their distinctive band structures, superlattice nanowires (NWs) have great potential as active materials for high-performance optoelectronic devices. In this work, IGZO NWs with superlattice structure and controllable stoichiometry are fabricated as photodetectors and their photoconducting property have been fully studied. Strikingly, when configured into individual NW photodetectors, the Ga concentration is found to significantly influence the amount of oxygen vacancies and oxygen molecules adsorbed on the NW surface, which dictate the photoconducting properties of the NW channels. Based on the optimized Ga concentration (i.e., In1.8Ga1.8Zn2.4O7), the individual NW device exhibits an excellent responsivity of 1.95 × 105 A/W and external quantum efficiency of as high as 9.28 × 107% together with a rise time of 0.93 s and a decay time of 0.2 s for the ultraviolet (UV) photodetection. Besides, the obtained NWs can be fabricated into large-scale parallel arrays on glass substrates as well to achieve fully transparent UV photodetectors, where the performance is on the same level or even better than many transparent photodetectors with high performance. All the results discussed above not only demonstrate a more comprehensive understanding of high-performance, solar-blind photodetector by crystalline IGZO NWs but also show the great potential of IGZO superlattice NWs for next-generation advanced optoelectronic devices.

    Research areas

  • InGaZnO, nanowires, thin-film transistors, superlattice, transparent, ultraviolet photodetectors