Optimization of metal-semiconductor-metal (MSM) photodetector arrays integrated with polyimide waveguides

The integration of MSM photodetector arrays with polyimide ridge waveguides is demonstrated. MSM detectors consisting of two Schottky interdigitated electrodes were fabricated singly and in arrays of two or four, on semiinsulating GaAs substrates. Following deposition and patterning of an SiO2 buffer layer, polyimide ridge waveguides were fabricated on top by spin coating and photolithography. The guides were multimode, with widths from 10 to 50 mu m, allowing for ease of coupling from an optical fiber. Light from the waveguides was coupled through gaps in the SiO2 buffer layer into the photodetectors. Transparent indium tin oxide (ITO) Schottky electrodes were employed to maximize absorption of light in the detector region. The end-to-end responsivities of the integrated MSM devices were typically 0.1 to 0.16 A/W. Bandwidths were 1 to 1.7 GHz; however these values could be increased substantially by optimization of the etch conditions used in the detector fabrication. Losses due to butt coupling to the multimode waveguides were around 1.5 dB. Division of the input signal between sets of two and four detectors has been demonstrated using a series of optical taps fabricated in an overlying polyimide ridge waveguide. Results indicate that polyimide waveguides could be a practical means of monolithically integrating optical functions such as signal routing and power division on complex optoelectronic integrated circuits (OEICs).