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 O-2 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 degrees C amorphous Ga2O3 films were deposited. Between 250 degrees C and 350 degrees C the films became predominantly alpha-Ga2O3. Above 350 degrees C the deposited films showed a mixture of alpha-Ga2O3 and epsilon-Ga2O3 phases. Plasma power and O-2 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 alpha-Ga2O3 phase deposited at 250 degrees C.