Conversion of p-type SnO to n-type SnO2 via oxidation and the band offset and rectification of an all-Tin oxide p-n junction structure

Abstract

p-Type Tin monoxide (SnO) is a metastable phase and can be oxidized into n-type SnO2 in an O2 environment during growth and post-growth annealing. Here we first grow SnO thin films by RF magnetron sputtering with different oxygen partial pressure in the sputtering gas followed by rapid thermal annealing (RTA) in O2 to obtain n-type conducting SnO2 films. We found that while after RTA in N2 stoichiometric SnO film is p-type conducting, films sputtered with excess O and RTA in O2 crystallize in rutile SnO2 structure and exhibit n-type conductivity. Exploiting the transformation of p-SnO to n-SnO2 through oxidation, we fabricate an all-Tin Oxide transparent p-n quasi-homojunction (p-SnO/n-SnO2) and compare it to a p-SnO/n-ZnO heterojunction structure in term of their rectification behavior. XPS measurements reveal that both SnO2 and ZnO at the Γ point exhibit a type II band offset with SnO with their respective valence band (conduction band) offset of 2.8 eV (1.9 eV) and 2.4 eV (1.33 eV). On the other hand, the indirect conduction band minimum of SnO shows a type I band offset in both junctions with a small conduction band offset of ∼0.1–0.17 eV. The SnO/SnO2 p-n structure shows a reasonable rectification with an ideality factor of ∼12.3, which can be potentially useful in many transparent p-n junction based devices.