The pulsed and steady-state photoresponses of silicon surface-barrier photodiodes having sensitive areas of 2.5 cm 2 have been measured at a photon wavelength λ of 850 nm (1.5 eV). The photodiodes studied are either windowless, i.e., have no gold film over the sensitive surface (no-gold photodiode), or have a thin (∼ 10 nm) gold film over the sensitive surface (gold photodiode). Local as well as broad-area photoresponses have been measured with the photodiodes operated in the reverse-bias mode. For comparison, pulsed photoresponses were also measured at λ = 337 nm (3.7 eV). The measured photocurrent pulses from no-gold photodiodes have a long time duration resulting from the large resistance and capacitance of the bare silicon surface. The results of these studies show that the characteristics of the measured photocurrent pulses from no-gold photodiodes are consistent with those expected for a model which treats the bare silicon surface as a two-dimensional RC line consisting of a homogeneously distributed capacitance and resistance and having circular geometry. Further, the results of steady-state photocurrent measurements and pulse amplitude measurements using pulse electronics with time constants in the range 5–1200 μs show that no-gold silicon photodiodes need no initial photon calibration. They serve as photon flux calibration detectors for both pulsed and steady-state photon sources provided the reflectivity of the no-gold photodiode is measured at the time of its use for a photon flux measurement. For the case of a pulsed photon source, the use of pulse electronics having time constants properly chosen to accommodate the slow current pulses from the no-gold photodiode is also required. Gold photodiodes may be calibrated easily by making use of a no-gold photodiode. The gold photodiode is calibrated by measuring photopulse amplitude ratios for pulsed photon sources or photocurrent ratios for steady-state photon sources. The pulse response of no-gold silicon photodiodes to charged particles has also been determined and the results compared with their response to pulsed photon sources and with the charged-particle response measured for gold photodiodes.