Abstract
The input wavelength dependence of the external quantum efficiency for InP/InGaAs uni-traveling-carrier photodiodes (UTC-PDs) was examined. A supercontinuum generated in the optical fiber was used as the monochromatic optical source with the wavelength ranging from 1.55 to 1.7 µm. The observed flatness of the efficiency shows the applicability of UTC-PDs to wide bandwidth transmission systems in which the bandwidths of the optical fiber and amplifier are fully utilized. It was also found that a UTC-PD with an acceptor doping density of 2.5×1018 cm-3 in the photo-absorption layer has a larger external quantum efficiency than a UTC-PD with a lower doping density at a wavelength around 1.7 µm. The mechanism of this enhancement is discussed based on the absorption coefficient and pulse responses measured at various input wavelengths.