Design and whole-wafer performance of separate absorption, grading, charge, and multiplication InP/InGaAs avalanche photodiodes

Avalanche photodiodes (APDs) are required for long distance fiber optical systems at wavelengths of 1.3 and 1.55 micrometers . Presently deployed systems operate at speeds up to 2.4 Gb/s, with increasing volumes. It is becoming increasingly necessary to produce low-cost, high-performance planar APDs. Most commercial InP/InGaAs APDs employ a separate absorption, grading, and multiplication (SAGM) design. However, this approach has severe process limitations for obtaining functioning APDs. Greater growth and processing flexibility is obtained from the separate absorption, grading, charge and multiplication (SAGCM) APD. In this work the influence of the layer thicknesses, junction depth and doping on the performance of SAGCM APDs is described both theoretically and experimentally. Theoretically, an analytical model of the (delta) -doped (ideal SAGCM) APD is presented, both neglecting and taking into account ionization in the InGaAs. In addition to the performance predictions with respect to fabrication parameters, this model also predicts that the gain depends on the wavelength of light (e.g. 1.3 or 1.55 micrometers ). Experimentally, whole 2-inch wafer performance results are interpreted with respect to variations in growth and processing parameters. The results are in good agreement with the predictions of the model.