Low noise GaAs-based avalanche photodiodes for long wavelength applications

Currently available avalanche photodiodes (APDs) for use in telecommunication systems operating at 1.3/1.55 μm utilize InP and InGaAs as the multiplication and absorption medium respectively. The excess noise performance of the InP avalanching region is relatively poor, and is limited by the hole to electron ionization coefficient ratio (β/α). We have recently reported that Al_0.8Ga_0.2As may be a suitable material for the multiplication region in APDs due to its large α/β ratio in bulk structures (B.K. Ng et al, IEEE Photon. Technol. Lett., vol. 14, p. 522, 2002), which results in a very low avalanche excess noise. In this work, we extend our previous study by investigating the excess noise characteristics in both bulk and sub-micron Al_xGa_1-xAs diodes as a function of x. Our results here suggest that long wavelength GaAs-based APDs of superior noise characteristics than InP-based APDs can now be realized.