An apparatus for estimating a property of a downhole fluid includes a carrier configured to be conveyed through a borehole penetrating the earth, a fluid extraction device disposed at the carrier and configured to extract a sample of the downhole fluid, and a probe cell having a window to receive the sample. The apparatus further includes a light source to illuminate the sample through the window with light photons, and a photodetector to receive light photons through the window that have interacted with the downhole fluid and generate a signal indicative of an amount of the received light photons. The generated signal is indicative of the property. The photodetector has an optical cavity having a semiconductor that has a difference between a valence energy band and a conduction energy band for electrons that is greater than the energy of each of the received light photons.