The　InP　cap　layer　plays　a　significant　role　towards　improving　the　performance　of　the　InP/InGaAs　p-i-n　photodiode.　However,　the　measurements　and　simulation　confirm　that　it　also　induces　wavelength-dependent　absorption　losses　and　a　non-flat　photo-responsivity　curve　due　to　the　reflections　from　a　multilayer　structure.