An Ag–GaAs Schottky-Barrier Ultraviolet Detector

Ag–GaAs Schottky-barrier photodiodes have been fabricated and evaluated as detectors of uv radiation. The quantum efficiency of these detectors is a maximum near 3225 Å, and is much less in the visible and ir regions of the spectrum. The peak quantum efficiency and selectivity of the detector is determined by the thickness of the silver layer, which possesses a narrow transmission ``window'' for radiation near 3225 Å wavelength. The transmittance of silver films evaporated on 7059 glass and quartz substrates was measured and compared with calculations based on previously published optical constants. At the transmittance peak, the extinction coefficient for these silver films was measured to be 0.38. From these transmittance measurements, the fraction of the radiation, incident on the silver, which enters the GaAs of the photodetectors was calculated as a function of wavelength and silver-film thickness. This quantity was compared with the measured quantum efficiency of the diodes. At the peak, the comparison indicated that 25–50% of the carriers created within the depletion region of the barrier do not contribute to the photocurrent. Measurements of the dependence of quantum efficiency on bias and energy of the absorbed radiation suggest that at the peak, a fraction of the carriers created within the depletion layer are energetic enough to pass over the Schottky barrier and not be collected as photocurrent.