Low temperature growth and optical properties of α-Ga₂O₃ deposited on sapphire by plasma enhanced atomic layer deposition

Plasma enhanced atomic layer deposition was used to deposit thin films of Ga₂O₃ on to c-plane sapphire substrates using triethylgallium and O₂ plasma. The influence of substrate temperature and plasma processing parameters on the resultant crystallinity and optical properties of the Ga₂O₃ films were investigated. The deposition temperature was found to have a significant effect on the film crystallinity. At temperatures below 200°C amorphous Ga₂O₃ films were deposited. Between 250°C and 350°C the films became predominantly α-Ga₂O₃. Above 350°C the deposited films showed a mixture of α-Ga₂O₃ and ε-Ga₂O₃ phases. Plasma power and O₂ flow rate were observed to have less influence over the resultant phases present in the films. However, both parameters could be tuned to alter the strain of the film. Ultraviolet transmittance measurements on the Ga₂O₃ films showed that the bandgaps ranges from 5.0 eV to 5.2 eV with the largest bandgap of 5.2 eV occurring for the α-Ga₂O₃ phase deposited at 250°C.