Increased power operation of GaAs/AlGaAs waveguide p-i-n photodiodes with non-absorbing input facets, fabricated by quantum well intermixing

Conventional vertical access photodiodes, where the light is input perpendicular to the plane of the absorbing layer, suffer from low efficiency at RF modulation frequencies due to the thin intrinsic absorption region required for short carrier drift times. Horizontal access as waveguide photodiodes (WGPD) and travelling wave photodetectors (TWPD), where light is guided along the absorbing layer for several absorption lengths, circumvent this problem and allow ~100% absorption of the input signal despite extremely thin depleted regions (~200 nm). One potential drawback of such devices is the catastrophic optical damage (GOD) which can occur at relatively modest power densities at the input facet of the waveguide. This is due to the temperature rise at the input facet. As many important applications of RF photodetectors require high power, this could be a severe limitation. Possible solutions to this problem include using very low absorption coefficient waveguides and the use of pseudo-window regions at the input facet. In the paper we present a simple method for producing a non-absorbing input facet function for a WGPD, or a TWPD, using quantum well intermixing (QWI) technology