Fabrication and characteristics of high performance SOI-based Ge PIN waveguide photodetector
- 物理技术－已发表论文 
本文报道了在SOI衬底上外延高质量单晶Ge薄膜并制备高性能不同尺寸Ge; PIN波导光电探测器.通过采用原子力显微镜、X射线衍射、拉曼散射光谱表征外延Ge薄膜的表面形貌、晶体质量以及应变参数,结果显示外延Ge薄膜中存在; 约0.2%左右的张应变,且表面平整,粗糙度为1.12 nm.此外,通过暗电流、光响应度以及3; dB带宽的测试来研究波导探测器的性能,结果表明尺寸为4 mum*20 mum波导探测器在-1 V的反向偏压下暗电流密度低至75; mA/cm~2,在1.55 mum波长处的响应度为0.58 A/W,在-2 V的反向偏压下的3 dB带宽为5.5 GHz.Silicon-based photonics has aroused an increasing interest in the recent year, mainly for optical telecommunications or optical interconnects in microelectronic circuits. The waveguide photodetector is one of the building blocks needed for the implementation of fast silicon photonics integrated circuits. The main considerations for designing such a device are the bandwidth, the power consumption and the responsivity. Germanium is now considered as an ideal candidate for fully integrated receivers based on silicon-on-insulator (SOI) substrates and complementary metal oxide semiconductor (CMOS)-like process because of its large optical absorption coefficient at the wavelength for optical communication. Therefore, the study of high speed and high responsivity Ge waveguide photodetectors is necessary. In this paper, high concentration phosphor doped SOI substrate is achieved by using solid-state source diffusion at first. Secondly, the high quality epitaxial germanium (Ge) is grown on phosphor doped SOI substrate by using low temperature Ge buffer layer technique based on the UHV/CVD system. The surface profile, crystal quality and strain of epitaxial Ge film are characterized by using atomic force microscopy, X-ray diffraction (XRD), and Raman scattering spectrum. The results show that the Ge film has a smooth surface of 1.12 nm roughness and about 0.2% tensile strain, which is verified by XRD characterization result. Thirdly, ptype Ge region is formed by BF2+ implantation, and rapid thermal annealing to repair the implantation damages and activate impurity. Finally, the highperformance Ge PIN waveguide photodetectors with different sizes are fabricated by standard COMS technology. Moreover, the device performances, in terms of dark current versus voltage characteristics, photocurrent responsivity and 3 dB bandwidth, are well studied. The results show that the detector with a size of 4 mu m x 20 mu m demonstrates a dark current density of 75 mA/cm(2) at -1 V and a photocurrent responsivity of 0.58 A/W for 1.55 mu m optical wavelength. In addition, an optical band width of 5.3 GHz at -2 V for 1.55 mu m is also demonstrated, which is far below theortical value of about 40 GHz. This can mainly be attributed to two aspects. On the one hand, Ge PIN structure contains low temperature Ge buffer layer, which has highdensity dislocation because of large lattice mismatch between Si and Ge. Those dislocations or defects can trap and release the photo-generated carrier, which increases the transit time. On the other hand, the contact characteristics of Al with n(+)-Si and p(+)-Ge are not very good, leading to a large contact resistance and RC delay. Through improving the above two aspects, the performance of Ge PIN waveguide photodetector will be further enhanced.