Evolution of the local structure and crystal phase for thin ZnGaO films grown by metal organic chemical vapor deposition

A systematic investigation is reported to comprehend the atomic and crystal structure of several thin ZnGaO films grown by metal organic chemical vapor deposition method using different flow rates of diethylzinc (DEZn) while keeping triethylgallium and oxygen flow rates constant. The x-ray absorption fine structure analysis has indicated that the local structure of Ga absorbing atom is close to that of beta-Ga2O3 at a lower DEZn flow rate of 30 sccm and transforming to ZnGa2O4 structure at higher 60 sccm. There is a certain proportion of Ga ions that occupies the tetrahedral sites. The ratios of tetrahedral and octahedral Ga species (Ga(t)/Ga(o)) are found to be within 5.5-8.8%. The x-ray diffraction patterns showed the crystal structure of ZnGaO films gradually evolving from monoclinic to cubic phase with an increase of DEZn flow rates from 30 sccm to 60 sccm. One film prepared at 40 sccm displays the best crystalline quality and the other grown at 50 sccm exhibits excellent smooth surface having the lowest root mean square value with a roughness of 0.42 nm. The correlation between atomic and crystal structure and the growth is helpful to understand the formation of single-crystalline ZnGa2O4 and its physical mechanism.