Fabrication and Characterization of Ga and N Co-Doped SnO2 Films by MOCVD

The gallium and nitrogen co-doped tin oxide (SnO2 :Ga-N) films have been prepared on α-Al2O3 (0001) substrates at 500°C by metalorganic chemical vapor deposition (MOCVD) method. The relative amount of Ga (Ga/(Ga+Sn) atomic ratio) was 8%. The flow rate of gaseous NH3 injected into the reactor chamber varied from 25sccm to 55sccm. According to the XRD patterns, the film grown at the flow rate of 25sccm has the best crystalline structure. Subsequently, a series of co-doped SnO2 films with the Ga concentration varying from 1% to 12% and the flux of 25sccm for NH3 were fabricated. Post-deposition annealing of the films was carried out at different temperatures for 2 h in nitrogen atmosphere. The structural, electrical and optical transmittance properties of the films have been investigated. For the as-deposited films, except that the film with 12% Ga doping has the amorphous structure, other films have the rutile structures of pure SnO2 with a strong (2 0 0) preferred orientation. After annealing, the structures of all films have changed obviously. Especially, the 12% Ga doping film has the polycrystalline structure also with the (200) preferred orientation. The average transmittances for all the films in the visible range were over 85%. The values of the band gaps varied from 3.3eV to 3.5eV for the as-deposited films and 3.7-3.9eV for the annealed ones. The electrical properties of the as-deposited films varied with the Ga content and were being discussed in detail.