The Role of the Schottky Metal in Optical Responses of Optical Position Sensitive Detector

The role of the Schottky barrier metal in position sensitive detector (PSD) formation is more complex than just acting to form a pseudo p-n junction and, in fact, it appears that it is the optical properties of this material that play a role in determining device performance. In this work titanium-silicon Schottky barrier PSDs were tested under 4 different wavelength LEDs and it was found that device performance was much better under long wavelength light. Along with the usual mechanisms, it is conjectured that this is related to the refractive index of the Schottky metal. PSDs with high sensitivities and strongly linear characteristics are much desired and many very high sensitivities have been reported upon by others, however, it is also important to consider the size of the linear region. The highest output measured here in response to 1 mW of LED light was 26 mV/mm over 9 mm surface path length. Shorter wavelength light has resulted in sensitivities which are significantly lower than the sensitivities obtained from longer wavelength light, but with higher linearities. The higher sensitivities are considered to be due to the absorption characteristics of the Schottky metal and this is attributed to recombination effects and differing transport paths that carriers take when illuminated by different wavelength light.