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 µm 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 µW. The rise time was measured to be 18 µs at P
in
= 10 µW. The noise characteristic was also measured for this device, and the resultant detectivity D
^*
was estimated to be 3.7 × 10
¹⁰
cm . Hz
^1/2
/W at a frequency of 2 kHz under an optical bias level of 0.1 µW. These characteristics have been theoretically discussed in detail.