Investigating the effects of package capacitance on the Frequency Response of Shallow Junction Avalanche Photodiodes

Shallow junction silicon avalanche photodiodes developed for photon-counting applications exhibit a multiplication gain of several hundred when operated near breakdown. The small size and relatively large gain of these devices identifies them as potential candidates for short-haul optical networking at 650nm. Of importance is the frequency response of these devices and in particular the limitations on achievable bandwidth placed by the packaging of the diodes. This work investigates the effect package capacitance has on the frequency response of Geiger Mode Avalanche Photodiodes (GMAP) when compared to micro-stripline mounted devices. Impulse response measurements are made of the diode using a pulsed laser diode at a wavelength of 650 nm which provides pulses with full-width at half maximum (FWHM) of 70 ps typical and 200 ps maximum. A Fast Fourier Transform (FFT) is applied to the measured pulse to convert it to the frequency domain and de-embed the response of the test fixture and cable assembly. The electrical parameters of the packaged and micro-stripline mounted devices are compared in the frequency domain to see the effect of the package capacitance on the frequency response. Different device geometries are explored to identify suitable candidates for short-haul plastic optical fibre communications.