High-Performance Electronics and Photodetectors Based on One-Dimensional Metal-Oxide Nanostructures


Student thesis: Doctoral Thesis

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Awarding Institution
Award date14 Dec 2018


One-dimensional (1D) metal-oxide nanowires (NWs) stimulated great interests in the scientific community in consequence of their extraordinary chemical and physical properties. These 1D materials are considered as the ideal systems to explore a great number of novel phenomena at nanoscale. In this regard, there are many efforts made to investigate the size and dimensionality dependence of these structures properties for various applications. Apart from evaluating their fundamental characteristics, these 1D metal-oxide nanostructures have also been used as active materials in fabricating electronic, optical, optoelectronic, electrochemical, and electromechanical devices, such assuch as photodetectors, single-electron transistors, electron emitters, field-effect transistors (FETs), light-emitting diodes (LEDs), biological and chemical sensors, as well as ultraviolet nanolasers. Here, utilizing in-situ Ga alloying, highly crystalline, uniform and thin In1.8Ga0.2O3 NWs with diameters down to 30nm are successfully prepared by ambient pressure CVD. Introducing the optimal amount of Ga (i.e. 10 at. %) into the In2O3 lattice is found to effectively enhance the crystal quality and reduce the oxygen vacancy concentration of the NWs. Further increase in the Ga concentration would adversely induce formation of resistive β-Ga2O3 phasecomposition, deteriorating electrical properties of the NWs. Importantly, when configured into global back-gated NW field-effect transistors (FETs), the optimized In1.8Ga0.2O3 NW FET exhibits the much enhancedmuch-enhanced electron mobility of up to 750 cm2V-1s-1 as compared with that of the pure In2O3 NW, which can be attributed to the suppressed oxygen vacancy concentration and reduced ionized impurity scattering centers. Highly ordered NW parallel arrayed devices are also fabricated to demonstrate the versatility and potency of these NWs for next-generation, large-scale and high-performance nanoelectronics, and sensors, etc.

Furthermore, less oxygen vacancy concentration induced by Ga alloying are found to strongly affect the photoconducting property of the NW. Usually, the practical application of photodetector based on oxide nanowires are limited by the long response time, low detectivity and responsivity. Photodetectors based on optimized Ga alloyed In1.82Ga0.18O3 NWs exhibit significantly enhanced responsivity of 1.92×105 A/W to ultraviolet (UV) light in comparison with In2O3 NWs, which is ascribed to the high electron mobility of the alloyed NWs. Meanwhile, the reduced oxygen vacancies in In1.82Ga0.18O3 NWs leads to fast response with rise time of 0.215 s and decay time of 0.248 s. Furthermore, the reduced oxygen vacancies also lead to a low dark current, thus high detectivity (6.78×1014 Jones). Our findings show that Ga alloying is an effective way to tune the optoelectronic properties of In2O3 NWs. They do not only present a more comprehensive understanding of high-performance, solar-blind photodetectors based on In2O3 NWs, but also reveal the versatility and potency of these NWs for next-generation optoelectronic devices.

At last, based on the InGaO NW FETs and photodetectors, change of electrical property and photosensing property with increase temperature are measured. With higher temperature, the drain-source current decrease and the off current increase, which lead to a dramatic suppression of the ON-OFF ratio. Meanwhile, the threshold voltage drop from -10V to -30V and the carrier mobility drop form 570 cm2V-1s-1 to 250 cm2V-1s-1. The subsequent increase is probably caused by the instability or leakage of current in subthreshold region. The photodetector exhibit the relatively stable performance with high temperature. The maximum value of responsivity can even reach are 4.5×105 A/W and 3.2×105 A/W under 120 ºC and 200 ºC. It is a very high value comparing to other kinds of harsh photodetector. All these results indicate that the InGaO NW is a qualified material for harsh electronics and photodetetors.