Monitoring　the　vacuum　ultraviolet　(VUV)　radiation　from　the　Sun　by　spaceborne　photodetectors　is　an　indispensable　and　crucial　approach　in　solar　physics　research　and　atmospheric　photochemistry　investigations.　Diamond-based　photodetectors　are　emerging　as　ideal　candidates　to　replace　traditional　silicon-based　detectors　for　high-selectivity　and　radiation　hardness.　Here,　a　vertical　Schottky　photodiode　based　on　p-type　high-quality　single-crystal　diamond　is　presented.　By　modulating　the　diamond　surface　band　structure　and　band　alignment,　an　ultra-short　response　time　of　only　15　ns,　and　a　photo-to-dark　current　ratio　greater　than　105　under　the　reverse　bias　are　achieved.　It　is　the　first　time　to　study　the　spectral　response　of　the　diamond　photodiode　in　the　range　of　260　nm　to　as　low　as　120　nm　under　vacuum　conditions,　exhibiting　an　ideal　selective　responsivity　and　excellent　imaging　capability　in　the　VUV　range.　This　device　holds　promising　prospects　for　coupling　with　optomechanical　systems　to　enable　a　multidimensional　detection　of　solar　VUV　radiation,　including　imaging　and　spectrum.