J. Phys. Chem. C 2010, 114, 1331–1336
1331
Aligned Tin Oxide Nanonets for High-Performance Transistors Cheng Sun,† Nripan Mathews,*,† Minrui Zheng,‡ Chorng Haur Sow,‡ Lydia Helena Wong,*,† and Subodh G. Mhaisalkar† School of Materials Science and Engineering, Nanyang Technological UniVersity, Blk N4.1, Nanyang AVenue, 639798, Singapore, and Department of Physics, National UniVersity of Singapore, 2 Science DriVe 3, 117542, Singapore ReceiVed: October 9, 2009; ReVised Manuscript ReceiVed: NoVember 19, 2009
Highly oriented tin oxide (SnO2) nanowire network (nanonets) based devices fabricated through photolithographyfree techniques are studied. These nanowire networks are studied at submillimeter scales for their utilization as the active material in thin film transistors for macroelectronics. The SnO2 nanowire network transistors show excellent device characteristics and possess electron mobilities of ∼7.5 cm2 V-1 s-1 and on/off ratios between 106 and 108 with channel lengths ranging from 75 to 175 µm. Exposure of the SnO2 nanonet transistors to the ambient results in positive threshold voltage shifts due to electron trapping by oxygen at the nanowire surface. On the contrary, the electrical properties of the devices remained unchanged upon passivation by a polystyrene (PS) layer, which demonstrates a practical way to enhance the device performance in air. These results suggest that SnO2 nanonets that offer fault tolerance, flexibility, and high transparency due to low areal coverage could be a suitable candidate for low-cost, large-area electronics. 1. Introduction In parallel to the rapid advancement of nanoelectronics, significant progress has been made in recent years to enlarge the system scale and create a new paradigm referred to as: macroelectronics or large-area electronics in which integrated microelectronics devices are fabricated over substrates ranging from several millimeters to meters in dimensions. Besides amorphous silicon (a-Si) and polycrystalline silicon (poly Si), which are commonly used as semiconductors, there has been growing interest in semiconducting nanostructures due to their potential applications on large-area, low-cost substrates fabricated using low-temperature or solution-based processes.1,2 Semiconducting nanostructures for field-effect transistors have included silicon,3 germanium nanowires,4 and carbon nanotubes.5 Another category of semiconductors gaining attention because of its low cost of growth and novel properties are metal oxide nanowires (NWs) including ZnO,6 In2O3,7 and SnO2. In particular, 1D tin oxide (SnO2) nanowires with a large band gap (3.6 eV) show significant potential for applications ranging from field-effect transistors,8,9 gas sensors,10,11 as well as solar cells.12 Oxygen vacancies and tin interstitials that have low formation energies create shallow donor levels lying below the conduction band and give rise to the high n-type conductivity of nonstoichiometric SnO2. Mobilities reported in both single crystal13 SnO2 (µ ) ∼250 cm2 V-1 s-1) as well as nanostructures14 (µ ) ∼125 cm2 V-1 s-1) are orders of magnitude higher than a-Si15 (
