Photovoltaic　solar-blind　ultraviolet　photodetectors　(SBPDs)　operate　independently　of　an　external　power　source,　addressing　critical　demands　in　extreme　environments,　such　as　forest　fire　detection　and　atmospheric　ozone　layer　monitoring.　Gallium　oxide　(Ga2O3)　offers　significant　potential　for　extreme　applications　due　to　its　radiation　resistance　and　high-temperature　stability.　Here,　we　present　a　novel　homoepitaxy　strategy　to　produce　an　＂atomic　smooth＂　step-flow　Ga2O3　photosensitive　layer,　successfully　fabricating　device-grade　Ga2O3/n+-Ga2O3　homojunctions　for　photovoltaic　SBPDs.　These　devices　exhibit　a　maximum　open-circuit　voltage　of　1.0　V,　an　ultrahigh　external　quantum　efficiency　of　59.5%,　and　an　ultrafast　response　time　of　100　ns　under　zero　bias,　maintaining　consistent　performance　even　at　390　K.　By　implementing　a　2D　step-flow　growth　mode,　both　bulk　and　interface　defects　were　effectively　suppressed,　achieving　the　desired　band　alignment.　Furthermore,　the　optimized　high-quality　depletion　region　formed　by　the　Ga2O3　layer　facilitates　enhanced　carrier　drift,　resulting　in　an　efficient　carrier　collection.　This　work　fully　explores　the　potential　of　Ga2O3　SBPDs　for　extreme　applications　and　provides　an　effective　design　strategy　for　achieving　photovoltaic　detectors　characterized　by　zero　power　consumption,　high　responsivity,　and　rapid　response.