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

•α-Ga2O3 can be grown directly from 200 °C to 400 °C; lower than for other techniques.•Morphology of Ga2O3 grown on sapphire by PEALD depends on the growth temperature.•Strain in the Ga2O3 film can be varied with deposition parameters.•α-Ga2O3 shows band gaps up to 5.2 eV. 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.