A systematic study of high-saturation-current p-i-n In0.53Ga0.47As photodiodes with a partially depleted absorber (PDA) has been made under front (p-side) and back (n-side) illumination. The photodiode structure consists of an In0.53Ga0.47As absorption region (450-nm p-InGaAs, 250-nm unintentionally doped InGaAs, and 60-nm n-InGaAs) sandwiched between p- and n-InP layers. For front illumination of a 34-μm-diameter photodiode at 2-V bias the saturation currents were 23 and 24 mA at 10 and 1 GHz, respectively. Under similar conditions, backside-illumination resulted in saturation currents of 76 mA (10 GHz) and >160 mA (1 GHz). Backside illumination of a 100-μm-diameter photodiode achieved a saturation current >400 mA. For the case of front illumination the device lateral resistance dominates whereas for backside illumination the response is determined primarily by the space charge effect.