InGaAsP/InP wavelength-selective heterojunction phototransistors

High-gain phototransistors with narrow spectral response (wavelength-selective phototransistors) have been developed by adding an absorption layer to a wide-bandgap heterojunction phototransistor using the InGaAsP/InP material system. The spectral response peaks at approximately 1.2 microns and the spectral half-width of 53 nm is achieved. This device exhibited an optical gain as high as 400 at the peak wavelength under an incident light power P(in) of 3.6 microwatts. The rise time was measured to be 18 microsec at P(in) = 10 microwatts. The noise characteristic was also measured for this device, and the resultant detectivity D(asterisk) was estimated to be 3.7 x 10 to the 10th cm sq rt of Hz/W at a frequency of 2 kHz under an optical bias level of 0.1 microwatt. These characteristics have been theoretically discussed in detail.