High-speed and high-saturation-current partially depleted absorber photodetecters [i.e. photodetectors

Abstract

For high power and high frequency optical links such as CATV, optical phased array antenna and photonic analog-to-digital converter systems, high linearity and large dynamic range are essential. In the digital domain, the highest sensitivities for 40Gb/s receivers can be achieved by incorporating an erbiumdoped-fiber-amplifier (EDFA) or semiconductor-optical-amplifier (SOA) directly in front of the photodetecter and eliminating the electrical post-amplifier. However, primary limiting factors for high-speed and high-saturation-current photodetecters are the space charge effect and thermal failure. A partially depleted absorber (PDA) photodiode is a novel approach that incorporates space charge balancing by placing a p-doped absorber and an n-doped absorber on each side of the i-region. The p-doped absorber injects electrons into the i-region while the ndoped absorber injects holes. Furthermore, the photodiode is designed with a thinned i-layer that reduces space-charge screening and minimizes thermal effects across the depletion layer. Since the PDA photodiode utilizes undepleted absorbing regions, it can accommodate thicker absorbing layers while simultaneously taking advantage of the thermal and space charge benefits of a thin depletion layer. A record high saturation-current bandwidth product was achieved. PDA photodiodes are promising for improving the performance of photoreceivers when the photodiodes are implemented with SOA in a waveguide structure. The second part of the dissertation contributes to a novel technique for calculating the gain distribution of an avalanche photodetecter by numerical solution of the recursive equations. This method yields the average gain, the multiplication noise, and gain distribution curves. The results were compared to previously reported measurements and simulations.