锗光电探测器与非晶硅基板上的非晶硅波导单体集成

Abstract: We present a proof-of-concept demonstration of a Ge/a-Si hybrid photonic  integrated circuit platform utilizing a high-quality Ge-on-insulator (GeOI) wafer fabricated by  wafer bonding technology. Amorphous Si (a-Si) formed by PECVD is found to be a  promising alternative to conventional Si passive waveguides on a SiO2 BOX. Taking  advantage of the high crystal quality of the Ge active layer and the easy fabrication of an a-Si  waveguide, a low-dark-current Ge waveguide PIN photodetector monolithically integrated  with an a-Si passive waveguide is successfully demonstrated on a GeOI wafer.

In recent decades, there has been significant progress in the field of Si photonics. Among  them, the introduction of a Ge thin film into Si-based platforms has proved to be a successful  approach, which enables not only new device functionalities but, more importantly, the  realization of various advanced systems on a single chip [1–4]. Ge has many advantageous  optical properties over Si. It exhibits strong optical absorption at wavelengths from 1.3 μm to  1.55 μm, making it ideal for photodetectors (PDs) in optical fiber communications [5–7]. A  large electro-absorption effect has also been observed in Ge, making it promising material for  realizing efficient optical intensity modulators [8,9]. Although Ge is an indirect-bandgap  semiconductor similar to Si, its direct bandgap is only 0.14 eV above the indirect bandgap at  the Γ valley. With the help of emerging band structure engineering technologies, it is even  possible to fabricate practical Ge-based light sources [10–13]. Thus, by realizing Ge active  photonic devices and Si passive devices, integration between Ge and Si provides a promising  means of achieving a cost-effective highly functionalized photonic integrated circuit (PIC)  platform, suitable for a wide range of applications.

Figure 1 illustrates the concept of Ge/a-Si hybrid PICs built on a GeOI wafer. A Ge  device layer with high crystal quality as well as strong optical confinement in the GeOI wafer  fabricated by wafer bonding allows us to develop high-performance, low-power, and compact  PICs for NIR wavelengths. In this paper, we present a proof-of-concept demonstration of a  Ge/a-Si hybrid platform on a GeOI wafer. First, we investigate Ge waveguide PDs on a GeOI  wafer. Then, monolithic integration between an a-Si waveguide and a Ge PD is achieved by  applying an optimized integration process, showing the feasibility of GeOI-based PICs with  a-Si waveguide interconnects for NIR photonics.

Fig1

For ease of measurement, a pair of focusing grating couplers is designed at both ends of  the a-Si waveguide, following a similar design methodology to that for conventional SOI  grating couplers [25]. Assuming the refractive index value of a-Si to be 3.7 [24], a grating  pitch of 560 nm, filling factor of 0.5, incidence angle of 9° and etching depth of 70 nm are  applied as the design parameters of the grating couplers with an a-Si layer thickness of 220  nm with the aim of achieving at a central wavelength of 1550 nm. In addition, grating  couplers and Si waveguides are also fabricated on an SOI wafer containing a 220-nm-thick Si  top layer and a 2-μm-thick SiO2 BOX for comparison.