High　electron　mobility　transistors(HEMTs)show　tremendous　potentials　for　high　mobility,　high　breakdownvoltage,　low　conduction,　low　power　consumption,　and　occupy　an　important　piece　of　the　microelectronics　field.The　high-resistivity-cap-layer　high　electron　mobility　transistor　(HRCL-HEMT)　is　a　novel　device　structure.Based　on　the　hole　compensation　mechanism,　the　p-GaN　is　converted　into　high　resistance　semiconductor　materialby　hydrogen　plasma　implantation.　Thus,　the　surface　of　the　p-GaN　layer　will　have　a　serious　bombardmentdamage　under　the　hydrogen　plasma　implantation.　In　practical　work,　it　is　also　very　challenging　in　the　accuratecontrolling　of　the　hydrogen　injection　rate,　injection　depth　and　injection　uniformity.　To　achieve　the　requireddepth　of　injection,　the　injected　hydrogen　plasma　is　often　more　than　the　required　dose　or　multiple　injectionstimes.　The　energy　of　hydrogen　plasma　plays　a　huge　influence　on　the　surface　of　the　p-GaN　layer.The　leakagecurrent　will　be　generated　on　the　device　surface,　which　deteriorates　the　electrical　performance　of　the　device.　In　this　work,　to　protect　the　surface　of　p-GaN　layer,　a　2-nm　Al2O3　film　is　deposited　on　the　surface　of　the　p-GaN　cap　layer　to　reduce　the　implantation　damage　caused　by　hydrogen　plasma　treatment.　The　research　showsthat　after　the　device　deposited　Al2O3　film　prior　to　the　hydrogen　plasma　treatment,　the　gate　reverse　leakagecurrent　is　reduced　by　an　order　of　magnitude,　the　ratio　of　ION　to　IOFF　is　increased　by　about　3　times.　Meanwhile,the　OFF-state　breakdown　voltage　is　increased　from　410　V　to　780　V.　In　addition,　when　the　bias　voltage　is　400　V,the　values　of　dynamic　RON　of　devices　A　and　B　are　1.49　and　1.45　respectively,　the　device　B　shows　a　more　stabledynamic　performance.　To　analyze　the　gate　leakage　mechanism,　a　temperature-dependent　current　IG-VG　testingis　carried　out,　and　it　is　found　that　the　dominant　mechanism　of　gate　leakage　current　is　two-dimensional　variablerange　hopping　(2D-VRH)　at　reverse　gate　voltage.　The　reason　for　reducing　the　gate　reverse　current　is　analyzed,and　the　Al2O3　film　increases　the　activation　energy　of　trap　level　and　changes　the　surface　states　of　HR-GaN;furthermore,　the　Al2O3　film　blocks　the　injection　of　too　much　H　plasma,　thereby　reducing　the　density　of　AlGaNbarrier　and　channel　trap　states,　and　weakening　the　current　collapse.