Electron transport properties of antimony doped SnO_2 single crystalline thin films grown by plasma-assisted molecular beam epitaxy

摘要

By antimony doping tin oxide, SnO_2:Sb (ATO), below 1.0% Sb concentration, controllable n-type doping was realized. Plasma-assisted molecular beam epitaxy has been used to grow high quality single crystalline epitaxial thin films of unintentionally doped (UID) and Sb-doped SnO_2 on r-plane sapphire substrates. A UID thickness series showed an electron concentration of 7.9 × 10~(18) cm~(-3) for a 26 nm film, which decreased to 2.7 × 10~(17) cm~(-3) for a 1570 nm film, whereas the mobility increased from 15 to 103 cm~2/V s, respectively. This series illustrated the importance of a buffer layer to separate unintentional heterointerface effects from the effect of low Sb doping. Unambiguous bulk electron doping was established by keeping the Sb concentration constant but changing the Sb-doped layer thickness. A separate doping series correlated Sb concentration and bulk electron doping. Films containing between 9.8 × 10~(17) and 2.8 × 10~(20) Sb atoms/cm~3 generated an electron concentration of 1.1 × 10~(18)-2.6 × 10~(20) cm~(-3). As the atomic Sb concentration increased, the mobility and resistivity decreased from 110 to 36 cm~2/V s and 5.1 × 10~(-2) to 6.7 × 10~(-4) Ω cm, respectively. The Sb concentration was determined by secondary ion mass spectrometry. X-ray diffraction and atomic force microscopy measurements showed no detrimental effects arising from the highest levels of Sb incorporation. Temperature dependent Hall measurements established a lower limit for the Sb electron activation energy of 13.2 meV and found that films with greater than 4.9 × 10~(19) electrons/cm~3 were degenerately doped. Within experimental uncertainties, 100% donor efficiency was determined for Sb-doped SnO_2 in the range studied.