Optimum Ge Profile Design for High-Response SiGe/Si Heterojunction Phototransistor Applicable in Wide Spectral Range of 400–1000 nm

In this article, different germanium (Ge) profile in SiGe base of SiGe/Si heterojunction phototransisitor (HPT) was analyzed and optimized to achieve high optical response in a wide spectral range of 400–1000 nm. A physical-based optical response model was developed considering the effect of Ge profile on the optical absorption and electrical amplification. The dependence of the optical absorption on the incident light wavelength in wide spectral range of 400–1000 nm also was discussed in this model. Three different Ge-distribution, including BOX, triangular and trapezoidal, and the total Ge-content in base were discussed to obtain the high optical responsivity and bandwidth in the wide spectral range based on the proposed model. The BOX Ge-distribution provide the maximum collector current and optical responsivity, meanwhile, the BOX Ge-distribution can achieve the 3-dB bandwidth close to the other two. The SiGe/Si HPT with BOX-Ge distribution and 0.16 total Ge-content were fabricated and achieved a better optical responsivity and bandwidth product, which presents well application potential in wide spectral range.