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We have fabricated and characterized two high-power high-linearity uni-traveling-carrier photodiode (UTC-PD) structures. The UTC performances are compared regarding their respective collector design. A -3-dB bandwidth improvement (from 16-25 GHz to 19-32 GHz) is achieved when the collector layer thickness is increased (from 250 to 350 nm, respectively). The bandwidth improvement for large photocurrent is at the origin of a ldquosupra-linearityrdquo effect. Photocurrent saturation effects are investigated and -1-dB compression current measurements at 20 GHz show saturation currents as high as 70 mA at -4 V. We also report third-order intermodulation distortion measurements at 20 GHz. The ldquosupra-linearityrdquo effect enhances the PD linearity with increased photocurrent, leading to a record third-order intercept point of 35 dBm at 40 mA.