UV light emitting transparent conducting tin-doped indium oxide (ITO) nanowires

Abstract

Multifunctional single crystalline tin-doped indium oxide (ITO) nanowires with tuned Sn doping levels are synthesized via a vapor transport method. The Sn concentration in the nanowires can reach 6.4 at.% at a synthesis temperature of 840 °C, significantly exceeding the Sn solubility in ITO bulks grown at comparable temperatures, which we attribute to the unique feature of the vapor-liquid-solid growth. As a promising transparent conducting oxide nanomaterial, layers of these ITO nanowires exhibit a sheet resistance as low as 6.4 Ω/[Symbol: see text] and measurements on individual nanowires give a resistivity of 2.4 × 10(-4) Ω cm with an electron density up to 2.6 × 10(20) cm(-3), while the optical transmittance in the visible regime can reach ∼ 80%. Under the ultraviolet excitation the ITO nanowire samples emit blue light, which can be ascribed to transitions related to defect levels. Furthermore, a room temperature ultraviolet light emission is observed in these ITO nanowires for the first time, and the exciton-related radiative process is identified by using temperature-dependent photoluminescence measurements.

Broad compositional tunability of indium tin oxide nanowires grown by the vapor-liquid-solid mechanism

“…3. This shift has also been observed in the case of ITO NWs obtained from the carbothermal reduction of In 2 O 3 and SnO 2 by Gao et al 5 The expanded view of the (222) reflection of In 2 O 3 depicted as an inset in Fig. 3 shows its dependence on the % In but contradicts Vegard's law which predicts a contraction in the host lattice due to the radius of the Sn 4+ ion (0.71Å) which is smaller compared to that of In 3+ (0.81 Å).…”

“…% ratio was 1%, 5%, 10%, 30%, 50%, and 90%. In contrast, Gao et al 5 Here we have grown ITO NWs on 1nm Au/Si(001) via the reaction of In and Sn with O 2 at 800 • C and 10 −1 mbar by varying systematically the In:In + Sn% weight ratio, hereafter denoted simply as % In, which was equal to 3%, 7%, 9%, 12%, 20%, 60%, 70%, 80%, and 100%. For 3% In, we obtained SnO 2 NWs with a tetragonal rutile crystal structure but between 3% to 9% In, we observe the existence of two distinct phases, i.e., SnO 2 with a tetragonal rutile crystal structure and cubic bixbyite In 2 O 3 due to the limited miscibility and different ionic radii of In and Sn.…”

“…[http://dx.doi.org/10.1063/1.4875457] Indium tin oxide (ITO) or Sn doped In 2 O 3 nanowires (NWs) are important as transparent conducting oxides (TCOs) for the fabrication of solar cells, [1][2][3] flexible displays, 4 and ultra violet light emitting diodes [5][6][7][8][9] because it has been suggested that higher Sn doping levels and conductivities can be attained in ITO NWs compared to bulk ITO. So far ITO NWs have been grown by carbothermal reduction of In 2 O 3 and SnO 2 5 but the control of stoichiometry is not trivial as it has been observed that SnO 2 NWs may be obtained even when a higher content of In 2 O 3 is used during carbothermal reduction carried out under an inert gas flow at elevated temperatures 10,11 which also leads to the non-intentional incorporation of carbon.…”

“…However, despite all of these efforts only few have investigated in detail the incorporation of Sn and the changes that occur in the crystal structure of ITO NWs by changing the In:Sn source ratio over a broad range. 5,12 For instance, Meng et al 12 obtained 20 at. % Sn in their ITO NWs using PLD by varying the In 2 O 3 :SnO 2 ratio of their target so that the corresponding Sn:In + Sn at.…”

“…3 shows its dependence on the % In but contradicts Vegard's law which predicts a contraction in the host lattice due to the radius of the Sn 4+ ion (0.71Å) which is smaller compared to that of In 3+ (0.81 Å). 5 This contradiction has been attributed to the large repulsive force arising from additional positive charges of the Sn cations 16,17 or to the increase of interstitial O which neutralizes the extra positive charges. 18 The variation of the lattice constant of (222), (123), (400), (411), (420), (332), (422), (134), (125), (440), (433), (600), (611), (026), (145), (622), (136), (444), (543), (046), (633), (156), (800), (811), (820), (653), (822), (831), (662), (048), (833), (248), (761), (158), (763), (844), (853), (1000) the ITO NWs with In content determined from the (222) reflection of In 2 O 3 is shown in Fig.…”