||In this study, transparent conductive oxide compound semiconductors, such as: InGaZnO(IGZO), ZnSnO(ZTO), and CuZnSnO(CZTO), were investigated and fabricated by using plasma-assisted molecular beam epitaxy. The content of gallium into IGZO thin films was adjusted to evaluate fundamental properties of IGZO. With Ga composition ratio higher than 27.9%, a phase transformation is observed from crystalline to amorphous. It was revealed redundancy metal which would self-assist channel or defect state to destroy crystal structure. The highest mobility 74.3 cm2/V-s was obtained at 27.9 atomic percentage of gallium by Hall measurement. The average optical transmittance is 80% in low Ga content(Ga < 18 at.%). By tuning element content of quaternary compounds, we obtained ternary plots distribution of IGZO thin films with different element content ratio. In:Ga:Zn:O thin film contents ratio relative to 1:1:1:4, respectively, was demonstrated at the amorphous structure. However, a crystalline of InGaO3(ZnO) thin film was reconstructed after 1100 °C annealing.
Transparent conductor oxide ZnSnO (ZTO) thin films were grown on c-sapphire by using plasma-assisted molecular beam epitaxy. Knudsen cell temperature of Sn was adjusted to verify content and discover the related thin films physic characteristic. Especially, the valence number of tin, i.e. Sn2+ and Sn4+, is correlated to the tin content in ZTO under oxygen poor condition was investigated. According to the X-ray diffraction results, two phase transformations are observed. When the metallic ratio of tin below 28.9 at.%, the crystalline of ZTO exhibits the Wurtize structure as well as ZnO. Additionally, the orientation signal (002) of ZTO shifts toward to small angle duo to the Zn2+substituted by Sn2+. Moreover, the relationship of lattice constant in c-axis and content ratio of tin obeys Vegard’s law. This region is defined as ZnO-SnO based. Further increasing the tin content, crystalline structure transfers to amorphous duo to the immerged of the distinct ZnO, SnO, and SnO2. Finally, when content ratio of tin reach 40 at.%, the excess of tin dominated and the SnO2 crystalline phase appeared. Environment assimilation resulting in less element behavior similar to majority, which explained Sn2+ existence in low tin content. The characteristics of ZTO, which took from atomic force microscopy, transmittance, photoluminescence, four-points Hall measurement, relates to the valence number of tin. The optical band gap decreases firstly and increases with arising tin content. A smooth ZTO surface may cause by surfactant effect from tin. The average transmittance in the visible spectra range is over 85 at.%. The lowest resistivity (4.53 × 10-3 ohm-cm) and the highest mobility (23.3 cm2/V-s) were obtained by four-point Hall measurement as tin content at 37.5 at.%. Temperature dependent Hall measurement implies conductivity mechanism similar to conductor in amorphous phase ZTO thin film.
P-type CZTO was successfully fabricated on c-sapphire by using plasma-assisted molecular beam epitaxy. CZTO thin film orientation peak was observed at 2θ= 34.49° which was presented element content of Cu, Zn, and Sn, as 11.36, 83.79, and 4.85 at.%, respectively. Phase transition which was demonstrated as crystalline to amorphous was occurred at TCu: 1100 oC(Cu=15.07 at. %) by XRD. SEM images, which was corresponded with XRD, verified phase transition from crystalline CZTO to co-exist of CZTO and ZnO. PL emission of CZTO with varition Cu and Sn content contain broad bands which corresponds to defect state emission of oxygen vacancy(Vo). Room-temperature optical transmittance of CZTO thin films reduced from 90% to 20% with Cu content increasing. Finally, p-type behavior CZTO thin film was obtained as carrier concentration of 1.6 × 1018 at TCu: 1200 oC.