This paper reviews the operation, design, and performance of the uni-traveling-carrier-photodiode (UTC-PD). The UTC-PD is a new type of photodiode that uses only electrons as its active carriers and its prime feature is high current operation. A small signal analysis predicts that a UTC-PD can respond to an optical signal as fast as or faster than a pin-PD. A comparison of measured pulse photoresponse data reveals how the saturation mechanisms of the UTC-PD and pin-PD differ. Applications of InP/InGaAs UTC-PDs as optoelectronic drivers are also presented.