High-Performance GalnAsP/InP Avalanche Photodetectors

High performance inverted-mesa GaInAsP/InP avalanche photodiodes responding out to 1.25 pm haye been fabricated. Uniform avalanche gains, M, of 700, dark current densities of 3 x 10-6 A/cm2 at M = 10, and an excess noise factor of -3 at M = 10 have been achieved by placing the p-n junction in the InP and using a new passivation technique. Pulse-response risetimes of less than 160 psec, limited by the risetime of the mode-locked Nd:YAG laser pulse, were measured with an avalanche gain of 40. Avalanche photodiodes (APDs) of the III-V quaternary alloy GaxIn1-xAsyP1-y on InP substrates have been under development in several laboratories for use in the 1.0-1.6 pm spectral region of interest for fiber optics applications. Typically, these devices, which have had the p-n junction located in the GaInAsP layer, have exhibited large values of dark current at biases sufficient to achieve gain, a condition that severely degrades the signal-to-noise performance and limits the gain to low values. Recently, however, Nishida et al. 1,2 have demonstrated in diffused structures that reductions in leakage current and increases in gain can be obtained by placing the p-n junction in the InP, so the high-field region is in the InP while the photogeneration region is in the GaInAsP. The noise performance of these devices was not discussed, but the low temperature (-190°C) noise characteristics of more conventional GaInAsP APDs were very recently published.3