Absorption region structure for unitraveling carrier photodiode

The invention provides an absorption region structure for a unitraveling carrier photodiode. The absorption region structure employs an In1-xGaxAsyP1-y material for growth, wherein the x and y express material components of a Ga element and a As element, the x is larger than 0 and is less than 1 and the y is larger than 0 and is less than or equal to 1; and the component parameters x and y change in a linear gradient mode or in a step type gradient mode, so that the gradient change of the forbidden band width in the absorption region is realized. Moreover, with selection of the component parameters x and y, the lattice constant of the In1-xGaxAsyP1-y material matches InP and the forbidden band width is not larger than that of photon energy of laser with the wavelength of 1.5 microns. According to the invention, with utilization of a built-in electric field introduced by a gradient energy band structure, the electric field intensity in the absorption region can be enhanced obviously; and the drift of electrons can be accelerated effectively based on the enhanced electric field and the transition time at the absorption region can be shortened. Therefore, the electron transition time in the absorption region of the unitraveling carrier photodiode can be reduced effectively. And utilization of the absorption region structure has the great significance in improving the bandwidth of the device and realizing the ultra-high-speed wireless communication system based on the device.