Optimization of Strain and Doping in Ge/GeSi Nanoscale Multilayers for GOI Short-Wave Infrared Imaging Applications

Area of Science:

• Optoelectronics
• Materials Science
• Semiconductor Physics

Background:

• Germanium (Ge)-based photodetectors are crucial for short-wavelength infrared (SWIR) applications.
• Optimizing n-type doping in Ge is challenging due to dopant out-diffusion and carrier recombination.
• Existing doping methods struggle to balance performance metrics like dark current and quantum efficiency.

Purpose of the Study:

• To develop an optimized n-type doping strategy for Ge-based PIN photodetectors.
• To achieve low dark current, high responsivity, and high quantum efficiency in the SWIR region.
• To investigate and compare in situ doping with ion implantation for the top absorbent layer.

Main Methods:

• Fabrication of Ge-on-insulator (GOI) substrates with multilayer structures (n+-Ge/i-Ge, n+-GeSi/i-Ge, n+-Ge/i-GeSi).
• Comprehensive material characterization using HR-XRD, SIMS, SEM, TEM, AFM, and PL.
• Comparison of in situ doping techniques with post-fabrication ion implantation for the n-type layer.

Main Results:

• In situ doping attempts were hindered by phosphorus (P) out-diffusion (segregation and auto-doping).
• Ion implantation proved effective for forming the n-type layer, overcoming doping challenges.
• Achieved peak responsivity of 0.99 A/W at 1550 nm, 79% external quantum efficiency, and low specific contact resistivities.

Conclusions:

• Ion implantation is a superior method for achieving high-performance n-type doping in Ge photodetectors compared to in situ methods.
• A combined strategy of multilayer/interface engineering and ion implantation optimizes optoelectronic properties.
• This approach enables the development of high-performance Ge-based SWIR photodetectors.