高速光探测器是高速光纤通信系统和网络中的关键器件，它要求光探测器具有宽的频率响应带宽和高量子效率。垂直入光型pin光探测器的高速性能和量子效率均受到吸收层厚度的限制。为了改善其高速性能，采用InGaAsP材料作为吸收层以及限制层渐变掺杂的方法，对垂直入光型pin光探测器的高速响应性能进行了理论研究和仿真，结果表明，高速响应达到了40GHz。与不采用渐变掺杂浓度的同种结构光探测器相比，高速响应性能显著提高。

As the key device for high bit rate optical fiber communication systems and optical networks, high speed photodetectors require wide frequency bandwidth and high quantum efficiency simultaneously. Vertically illuminated pin photodetector suffers such a tradeoff as the frequency response and quantum efficiency are both limited by the thickness of the absorption layer. To improve its highspeed performance, InGaAsP is used as the absorbing material and the cladding layer is graded doped. In this paper, the high speed response performance of the vertically illuminated pin photodetector is optimized by theoretical studies and simulation analysis, and its 3dB bandwidth reaches 40GHz. Compared to the photodetector without applying graded doping, the high speed performance is significantly improved.