High-gain low-noise GaAlAs-GaAs phototransistors

GaAlAs-GaAs heterojunction phototransistors designed for a high sensitivity have been fabricated. Very large current gains have been observed (over 104), together with moderate input capacitances (about 5 pF). With these figures bipolar phototransistors appear as real candidates for low-noise large-bandwidth optical receivers; from signal/noise measurements on large devices, a minimum detectable power of −34.5 dBm at 0.82 μm was evaluated for a 140 Mbit/s data rate