InP/InGaAs heterojunction phototransistors

We describe the fabrication and device characteristics of experimental back-illuminated InP/InGaAs n-p-n heterojunction phototransistors. These devices exhibit photoresponse in the wavelength range of
0.95-1.6 \mu
m. An optical gain of 40 at an input power of 1 nW (an improvement of 1000 in sensitivity over previously reported phototransistors) has been observed. Gains as high as 1000 have been achieved for higher incident power levels.