Gallium　oxide　(Ga2O3)　thin　films　were　prepared　on　c-plane　sapphire　substrates　by　plasma　enhanced　atomic　layer　deposition　(PEALD).　The　effects　of　annealing　atmosphere　(v(N2):　v(O2)=1:　1　(volume　ratio),　Air　and　N2)　and　annealing　time　on　the　crystal　structure,　surface　morphology　and　optical　properties　of　Ga2O3　films　were　studied.　The　research　results　indicate　that　gallium　oxide　is　in　metastable　state　before　annealing,　and　the　crystal　structure　changes　significantly　after　annealing　in　different　annealing　atmospheres,　and　the　increase　in　the　proportion　of　N2　in　annealing　atmosphere　is　beneficial　to　the　recrystallization　of　Ga2O3.　Furthermore,　the　effect　of　annealing　time　was　further　studied　under　N2　atmosphere,　and　the　results　show　that　the　structure　of　the　thin　film　changes　from　metastable　state　to　β-Ga2O3　with　good　single　orientation　after　annealing　for　30　min　in　N2　atmosphere.　And　the　surface　morphology　analysis　show　that　the　surface　morphology　begins　to　stabilize　after　annealing　for　30　min,　and　the　surface　grain　density　no　longer　increases.　In　addition,　the　average　transmittance　of　the　sample　in　the　range　of　400　nm　to　800　nm　is　almost　100%,　and　the　light　absorption　edge　is　steep.　Annealing　in　N2　atmosphere　is　more　conducive　to　the　migration　of　atoms　on　the　surface　of　the　film　for　Ga2O3　deposited　in　an　oxygen-rich　environment,　and　Ga2O3　recrystallization　is　preferred.　©　2021,　Journal　of　Synthetic　Crystals　Press.　All　right　reserved.