Abstract
In this work we study, using experiments and theoretical modeling, the mechanical and optical properties of tensile strained Ge microstructures directly fabricated in a state-of-the art complementary metal-oxide-semiconductor fabrication line, using fully qualified materials and methods. We show that these microstructures can be used as active lasing materials in mm-long Fabry-Perot cavities, taking advantage of strain-enhanced direct band gap recombination. The results of our study can be realistically applied to the fabrication of a prototype platform for monolithic integration of near infrared laser sources for silicon photonics.
Highlights
The realization of a Si-integrated light source represents today the “Holy Grail” of silicon photonics
In tensile strained Ge layers, this energy difference is reduced owing to the different deformation potentials of the conduction band minima, with an indirect-to-direct band gap crossover predicted to occur at ε~2 × 10−2 [4,5,6]
In this work we demonstrate a complementary metal oxide semiconductor (CMOS) based fabrication approach to obtain Ge microstripes on Si wafer with equivalent biaxial tensile strain values up to ε ~9 × 10−3
Summary
The realization of a Si-integrated light source represents today the “Holy Grail” of silicon photonics. The recent demonstration of optically [2] and electrically [3] pumped Ge-based laser fabricated on a Si substrate has been welcomed in the scientific community as a leap toward the achievement of a monolithically integrated silicon-based photonic platform. In order to engineer the optical properties of the Ge active material, the authors exploited a combination of moderate biaxial tensile strain (ε~2 × 10−3) and heavy n-type doping (ndop>4 × 1019cm−3). Germanium is a quasi-direct band gap semiconductor, featuring a Γc-Lc valley energy separation of only ~135 meV [4,5,6]. In order to address this major issue, two different routes can be considered: ultra-high doping density and/or increased tensile strain [7]
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