Mingjie Cao

Preparation and Characterization of Cu(In,Ga)Se2 Thin Films by Selenization of Cu0.8Ga0.2 and In2Se3 Precursor Films

Se-containing precursor films with two different compositions were prepared by magnetron sputtering from and targets, and then were selenized using Se vapor. The effects of precursor composition and selenization temperature on the film properties were investigated. The results show that Se phase plays a critical role in film growth and electrical properties of CIGS films. The Cu-rich films exhibit different surface morphology and better crystallinity, as compared to the Cu-poor films. All the CIGS films exhibit p-type conductivity. The resistivity of the Cu-rich films is about three orders of magnitude lower than that of the Cu-poor films, which is attributed to the presence of p-type highly conductive Se phase.

Reaction Mechanism of Cu(In, Ga)Se2 Formation During Milling Process of Powder Mixture of Cu2Se, In2Se3 and Ga2Se3

Sputtering targets of CIGS quaternary ceramic were fabricated by hot-press sintering the milled powder mixture of Cu2Se, In2Se3 and Ga2Se3. When the milling time of the powders less than 4 h, the sintered targets delaminated, while the delamination disappeared with the prolonging milling time. Therefore the physico-chemical changes of the powder mixture during the milling process and their influence on the delamination of the targets were investigated. The results indicate that with the progress of the milling process, mechanical alloying (MA) occurred, and chalcopyrite Cu(In, Ga)Se2 (CIGS) formed from Cu2Se, In2Se3 and Ga2Se3; With the increasing milling time, CuInSe2 (CIS) formed on the surface of binary copper selenide firstly and CIGS was subsequently generated due to the inward diffusion of Ga; Thus the original blend powders became a mixture of CIGS and residual Ga2Se3 after milling for 48 h. Since CIGS and Cu2-xSe have a similar crystallographic structure, therefore this epitaxial relation may facilitate the formation of CIGS. The disappearance of Cu-Se binary compound and the formation of CIGS restrained the delamination of the CIGS targets in the sintering process.

Electronic Properties of Amorphous Indium-gallium-zinc Oxide Thin Film Fabricated by Magnetron Sputtering

Amorphous indium- gallium- zinc oxide(a- IGZO) thin films were fabricated using mid- frequency AC magnetron sputtering deposition with variable oxygen flow rate and sputtering current. The influence of processing parameters on the electronic properties of the films was investigated by means of analyses of XRD and XRF, as well as Hall Effect measurement. The results show that all the samples are amorphous with compositions roughly equal to that of the target. The change of sputtering current had no significant effect on the electronic properties. But the carrier concentration of the samples exhibited an obvious change as the increase of the O2 flow rate, which slightly increased and then rapidly decreased.The samples with higher carrier concentration exhibited larger Hall mobility. The average transmission of the IGZO thin films deposited with large O2 flow rate is above 90%.

Influence of Annealing Temperature on Electric Properties of CuIn1-xGaxSe2 Thin Films

The as-deposited CuIn1-xGaxSe2(CIGS) thin films were fabricated by magnetron sputtering from a quaternary CIGS target, and then the as-deposited films were annealed in a temperature range from 240℃ to 550℃. The effect of the annealing temperature on the electric properties(carrier concentration and carrier mobility) of the films was investigated in particular. The results show that when the annealing temperature was lower than 270℃, the highly conducive CuSe phase existed in the films leading to a high carrier concentration(1017-1019cm-3) and a low carrier mobility(~0.1 cm2·V-1·s-1). These films are not suited for CIGS absorber usage. When the annealing temperature was higher than 410℃, the carrier mobility of the films was high about 10 cm2·V-1·s-1and the carrier concentration was in a range of 1014-1017cm-3due to the disappearance of the CuSe phase. When the annealing temperature was higher than 410℃,with the increase of the annealing temperature the grains grew larger and the crystallinity of the films was enhanced, which could reduce the defects in the films and result in the decrease of the carrier concentration. From the aspect of the carrier concentration and the carrier mobility, the appropriate annealing temperature for fabricating the absorbers of the CIGS solar cells is from 450℃ to 550℃.