Research on p-SnO Films and Electronic Devices of NIMTE Achieved

Series Progress

Thin-film transistor (TFT) is a kind of semiconductor device which has widespread application value and prospect in fields of information display and transducer. The wide-band oxide semiconductor gained much attention recently with many advantages such as low temperature filming, high electron mobility and high optical transparency in the visible range. The p-type and n-type conductivity materials both are important for the development of TFT. However, the fabrication of p-type conductivity materials is becoming a major bottleneck.

The p-type conductivity of SnO was suggested to originate from the tin vacancy, and it can be improved via proper doping. Those properties make SnO a promising candidate to be a p-type oxide semiconductor utilized for applications in areas such as photovoltaics, electronics, displays, sensors, and information storage. Post-Doc Ling Yan Liang and Prof. Hong Tao Cao and Xiao Qing Pan from Functional Materials and Nano Devices Division of Ningbo Institute of Materials Technology and Engineering (NIMTE) fabricated single-phase polycrystalline SnO thin films on quartz by a two-step method (see Fig.1). Its photoelectron properties (see Fig.2) and valence electron structure (see Fig.3) were also studied. Part results of the studies were published in journal of ACS (ACS Appl. Mater. Interfaces, DOI: 10.1021/am900838z) and in journal of ECS (J. Electrochem. Soc., 2010, 157, H598). Figure 4 shows the output curves of the TFTs employing polycrystalline SnO channels.

Under the collaboration of research team leading by Prof. Hong Tao Cao and research team leading by Prof. Xiao Qing Pan from University of Michigan, SnO thin films were fabricated by electron beam evaporation on (100) Si and c- and r-plane Al2O3 substrates. The films grown at 25 °C are nano-crystalline, while the films grown at 600 °C are epitaxial on r-plane Al2O3 and (001) textured on Si and c-plane Al2O3. The SnO films have an optical band gap of 2.82–2.97 eV and p-type conductivity, according to Hall measurements, with resistivity of 0.5–110Ωcm, hole concentrations of 1017–1019 cm−3, and Hall mobilities of 0.1–2.6 cm2/Vs. The p-type conductivity, which appears to correlate with VSn, can be enhanced via Y- and Sb-doping. Defect complexes of SbSn−2VSn are suggested to be the acceptors in Sb-(or Y-) doped SnO films.

This work was financial supported by the key project of the Natural Science Foundation of Zhejiang province, P. R. China, and the Special Foundation of President of Chinese Academy of Sciences.