Effect of sodium doping on characteristics of p-SnOx films prepared by reactive direct current magnetron sputtering

Abstract

Conventionally, p-type semiconducting oxide films of high optical transmission and good electric conduction are materials of great demand in electronic and optoelectric devices. They can conveniently be integrated with their n-type counterparts for formation of homo or heterojunctions. In this report, Na-doped SnOx films were fabricated by reactively sputtering the Sn + Na alloy targets at substrate temperature of 200 °C. Effect of Na dopant concentration on crystal structure, electric and optical properties of Na-doped SnOx films was investigated with X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, atomic force microscopy, Hall and UV–Visible transmission spectroscopy. The obtained results revealed that when Na + substituted Sn2+, the hole concentration increased but the crystallite size reduced, leading to increased grain boundary and reduced carrier mobility. However, electric resistivity still reduced thanks to the increase of carrier concentration. Averange optical transmission of Na-doped SnOx films in visible range was approximately 65%. In addition, optical bandgap value reduced as Na doping amount in those films increased. The Na-doped SnOx films sputtered from Sn + 3 at% Na alloy targets, corresponding to 1.56 at% Na existing in films, presented the best electric property (nH = 2.75 × 1019cm−3, μ = 2.4 cm2/VS, ρ = 9.35 × 10−2Ωcm). This film proceeded with diode structure of glass/FTO/n-nc-Si:H/p-SnOx:Na/Cu, resulted in the best characteristics (VOC = 0.59 V, n = 3.57, rectifying ratio = 22, Rs = 38.1 Ω).