Ultrasensitive Si phototransistors with a punchthrough base

Si phototransistors with a punchthrough base were fabricated with regular planar technology. Optical conversion gains larger than 15 000 were observed. In addition to very high gain, the unique structure of the device also resulted in a fast transient response as well as low output noise. The measured full width at half maximum of the device transient response is 1.6 ns and a -3 dB bandwidth of 300 MHz. The measured output noises at different currents can be well fitted by the relation i(n)((2) over bar)=2qI(C). (C) 2001 American Institute of Physics