Si/Ge　uni-traveling　carrier　photodiodes　exhibit　higher　output　current　when　space-charge　effect　is　overcome　and　the　thermal　effects　is　suppressed.　High　current　is　beneficial　for　increasing　the　dynamic　range　of　various　microwave　photonic　systems　and　simplifying　high-bit-rate　digital　receivers　in　many　applications.　From　the　point　of　view　of　packaging,　detectors　with　vertical-illumination　configuration　can　be　easily　handled　by　pick-and-place　tools　and　are　a　popular　choice　for　making　photo-receiver　modules.　However,　vertical-illumination　Si/Ge　uni-traveling　carrier　(UTC)　devices　suffer　from　inter-constraint　between　high　speed　and　high　responsivity.　Here,　we　report　a　high　responsivity　vertical-illumination　Si/Ge　UTC　photodiode　based　on　a　silicon-on-insulator　substrate.　When　the　transmission　of　the　monolayer　anti-reflection　coating　was　maximum,　the　maximum　absorption　efficiency　of　the　devices　was　1.45　times　greater　than　the　silicon　substrate　owing　to　constructive　interference.　The　Si/Ge　UTC　photodiode　had　a　dominant　responsivity　at　1550　nm　of　0.18　A/W,　a　50%　improvement　even　with　a　25%　thinner　Ge　absorption　layer.