InGaAsP photodiodes

The low carrier concentration materials required for high-sensitivity p-i-n and avalanche InGaAsP photodiodes can be grown by the techniques of liquid phase epitaxy and by those of vapor phase epitaxy. It is shown that the dark current of these devices can be dominated by tunneling through defect states. Large leakage currents in avalanche photodiodes are virtually eliminated by the separate absorption/multiplication diode structure. The excess noise factor of the multiplication process is found to be in good agreement with that calculated from the electron and hole impact ionization coefficients alpha and beta. Even though the excess noise is high because of the nearly equal values of alpha and beta, InGaAsP avalanche photo-diodes can still increase significantly the performance of wide-bandwidth fiber-optical systems.