• PDF / 306,320 Bytes
• 6 Pages / 584.957 x 782.986 pts Page_size
• 32 Downloads / 223 Views

DOWNLOAD

REPORT

---

kashi Yagi and Naoyuki Taketoshi National Metrology Institute of Japan, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8563, Japan

Junjun Jia and Yuzo Shigesatob) Graduate School of Science and Engineering, Aoyama Gakuin University, Chuo, Sagamihara 252-5258, Japan (Received 1 April 2014; accepted 11 July 2014)

We investigate the effect of dopant species and structure on the thermal conductivity of Sb-doped SnO2 (ATO) and Ta-doped SnO2 (TTO) films and compare the results with those of In2O3-, ZnO-, and TiO2-based transparent conductive films. The thermal conductivities (k) of polycrystalline ATO and TTO films are 4.4–4.9 and 4.7 W m 1 K 1, respectively. The thermal conductivities via phonons (kph) are almost identical for both dopant species (Sb and Ta): 4.3 and 4.5 W m 1 K 1 for Sb and Ta, respectively, on average. These results for kph are larger than that for Sn-doped In2O3 films (3.8 W m 1 K 1) and considerably larger than that for amorphous ATO films (1.0 W m 1 K 1). These facts lead us to conclude that the base-material species (SnO2 or In2O3) and structure (polycrystalline or amorphous) affect the thermophysical properties of ATO and TTO much more than the dopant species.

I. INTRODUCTION

SnO2-based transparent conductive oxide (TCO) films, such as Sb-doped SnO2 (ATO),1–7 are the most chemically stable among TCO materials—an important prerequisite for several applications, such as solar cells. However, as Sb is undesirable for industrial applications because of its toxicity, it is important to find alternative doping materials. Among the possible alternative candidates, Ta shows promise, as demonstrated by a recent report in which heteroepitaxial Ta-doped SnO2 (TTO) films exhibited low resistivity (1.1  10 4 X cm).8 A thermal design is important for optoelectronic devices composed of distinct films, such as organic light-emitting diodes (OLEDs) and solar cells because the luminescence and power-generation efficiencies, respectively, decrease with increasing temperature.9–11 An effective thermal design thus requires highly accurate data on the thermophysical properties of the device’s constituent layers, and some such data are available. For example, the thermal Address all correspondence to these authors. a) e-mail: [email protected] b) e-mail: [email protected] c) Present affiliation: Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1 Katahira, Aoba, Sendai 980-8577, Japan. e-mail: [email protected]. This paper has been selected as an Invited Feature Paper. DOI: 10.1557/jmr.2014.191 J. Mater. Res., Vol. 29, No. 15, Aug 14, 2014

http://journals.cambridge.org

Downloaded: 17 Mar 2015

diffusivities of Sn-doped In2O3 (ITO) and In2O3–ZnO (IZO) films, both widely used as TCO films, have been reported. For 200-nm-thick ITO and IZO films, the thermal diffusivities are (1.5–2.3)  10 6 and (0.63–1.4)  10 6 m2 s 1, respectively, and are proportional to the electrical conductivities.12,13 However, comparable data for ATO and