A MONTE-CARLO INVESTIGATION OF MULTIPLICATION NOISE IN THIN P(-I-N(+)GAAS AVALANCHE PHOTODIODES())

A Monte Carlo (MC) model has been used to estimate the excess noise fa ctor in thin p(+)-i-n(+) GaAs avalanche photodiodes (APD's), Multiplic ation initiated both by pure electron and hole injection is studied fo r different lengths of multiplication region and for a range of electr ic fields. In each case a reduction in excess noise factor is observed as the multiplication length decreases, in good agreement with recent experimental measurements. This low noise behavior results from the h igher operating electric field needed in short devices, which causes t he probability distribution function for both electron and hole ioniza tion path lengths to change from the conventionally assumed exponentia l shape and to exhibit a strong dead space effect. In turn this reduce s the probability of higher order ionization events and narrows the pr obability distribution for multiplication, In addition, our simulation s suggest that for a given overall multiplication, electron initiated multiplication in short devices has inherently reduced noise, despite the higher feedback from hole ionization, compared to long devices.