A metal-PbSe-clad BaF2 waveguide photodetector

We have analyzed a metal-PbSe-clad waveguide structure for use as a photodetector in the 3–5 μm wavelength range. Operation of the photodetector is based upon achieving a high degree of coupling of the energy from guided modes supported by the BaF2 waveguide into lossy modes supported by the PbSe cladding. The energy is absorbed in the PbSe, producing excess charge carriers that are collected by the metal electrode. The cutoff conditions, mode indices, and attenuation values for the TE and TM modes were determined as a function of the PbSe thickness for a free space wavelength of 3.4 μm. The critical value of PbSe thickness that leads to maximum attenuation of the TE0 mode was investigated for metal electrode layers of varying composition and thickness. We have found that maximum attenuation of the TE0 mode is achieved for an optimized photodetector structure in which the PbSe thickness is 45 nm and the metal electrode consists of a 4 nm thick layer of platinum.