A phototransistor with concentric electrodes on the Si substrate

A high-speed phototransistor with concentric lateral electrodes was fabricated on the Si substrate. The optical gain for continuous wave He-Ne laser excitation can be as high as 80. The pulse width in response to mode-locked laser pulses is 220 ps. A bandwidth of 1.7 GHz was observed for saturated unity-gain operation. The capability of being integrated is potentially useful in realizing high-speed optical receivers.