Carrier doping into MgIn2O4 epitaxial thin films by proton implantation

Epitaxial thin films of MgIn2O4 were grown on MgO(100) single-crystal substrates through the pulsed laser deposition technique. X-ray diffraction measurements revealed film orientations MgIn2O4(h00)//MgO(h00) and MgIn2O4(0k0)//MgO(0k0), respectively. Proton implantation was applied to generate carrier electrons in the films. The electrical conductivity of the as-deposited films is below ∼10−7 S cm−1 at room temperature. The maximum conductivity of ∼70 S cm−1 was obtained by the implantation. Hall voltage measurements revealed that H+ implantation causes carrier generation in proportion to H+ fluence without reduction of electron mobility. Following the post-annealing process resulted in further enhancement of the conductivity in each H+-implanted film, as conductivity and generation efficiency were found to increase up to ∼2×102 S cm−1 and ∼95% at the maximum, respectively. This differs from the behavior of polycrystalline films in which conductivity decreased by post-annealing due to a decrease in the Hall mobility of electrons. Thus it is concluded that crystal quality is crucial for heavy carrier doping by ion implantation, especially when utilizing post-annealing treatments to enhance the carrier generation efficiency without reduction of the Hall mobility.