From stannous oxide to stannic oxide epitaxial films grown by pulsed laser deposition with a metal tin target

Stannous oxide (SnO) and stannic oxide (SnO2) are both important wide-band-gap semiconductors. To study the conductive mechanism in detail, high quality epitaxial films are essential. Here we propose a simple method to grow high quality epitaxial films of either stannous oxide or stannic oxide on an r-plane sapphire substrate by using pulsed laser deposition with a metallic tin target. The valence state of tin is controlled by tuning the oxygen pressure during the deposition procedure. Metal tin impurities and the transition phase of Sn3O4 are avoided and the growth windows from stannous oxide to stannic oxide are confirmed. For single-crystalline SnO epitaxial film, a rocking curve half-width of 0.22° is obtained, which is better than the 0.46° of that on a YSZ substrate. The minimum roughnesses achieved were 0.37 nm for the SnO2 epitaxial film and 0.84 nm for the SnO epitaxial film. The epitaxial relationship between SnO and the r-sapphire substrate was determined to be SnO [1¯10]//sapphire [1¯21¯0] and SnO [1 1 0]//sapphire [101¯1]. For SnO2, the epitaxial relation is SnO2 [0 1 0]//sapphire [1¯21¯0] and SnO2 [1¯01]//sapphire [101¯1]. The band schematics, deduced by combined XPS valence band spectroscopy and optical transmittance spectroscopy, indicated p-type bands of SnO and n-type bands of SnO2. Raman spectroscopy is suggested to be a superior fingerprint of SnO single-crystalline quality, due to its greater sensitivity than X-ray diffraction.