Performance comparison of heterojunction phototransistors, p-i-n FET's, and APD-FET's for optical fiber communication systems

An analysis of the sensitivity of InGaAs/InP bipolar heterojunction phototransistors (HJPTs) used in pulse code modulated optical communication systems is presented. The minimum detectable power of an HJPT biased at the optimum level is found to increase linearly with bit rate
B
while because of the fixed transconductance of the FET amplifier, the minimum detectable power of a p-i-n FET increases as
B
^3/2
. It is shown that HJPTs can thus have higher sensitivity than p-i-n FET detectors, particularly at high bit rates, and can have comparable sensitivity to ADP-FET detectors.