Search

In this work, we propose aninitial framework and present numerical estimates for designing a GeSn-based quantum well (QW) laser that can attain efficient lasing, while utilizing a monolithic lattice matched (LM) InGaAs/GeSn/InGaAs stack. GeSn QW emission characteristics depend significantly on the quantized energy level as the bulk bandgap reduces and approaches zero for high Sn. One factor that diminishes the quantum efficiency of light sources is the defects present within the active region, which result in non-radiative recombination. Furthermore, defects at the interface can hinder the band alignment causing loss of carrier confinement. InGaAs, InAlAs and a well-designed LGB can provide large band offsets with GeSn to form a type I separate confinement heterostructure (SCH) QW laser structure while enabling a virtually defect-free active region suitable for room temperature operation and scalable to an arbitrary number of QWs. When LM, the InAlAs and InGaAs layers provide a large total band offset of ∼1.1eV and ∼0.6eV, respectively. For a 10 nm GeSn QW SCH laser, a threshold current (JTH) of ∼10 A/cm2 can be achieved at an emission wavelength of ∼2.6 μm with a net material and modal gain of ∼3000 cm−1 and ∼40 cm−1, respectively. The JTH and net gain can be optimized for the InAlAs/InGaAs/GeSn/InGaAs/InAlAs SCH laser structure for Sn between 8--18% by adaptively designing the SCH waveguide and QW. Through adaptive waveguide design, quantization, and Sn alloying, a wide application space (1.2 μm to 6 μm) can be covered.

Here, we have analyzed the electrical and optical phenomenon occurring in a ϵ-Ge/InxGa1-xAs quantum well (QW) laser through self-consistent physical solvers calibrated using in-house experimental results. A separate confinement heterostructure QW design is proposed to enable lasing from tensile strained germanium (ϵ-Ge) in the range of 1.55 μm to 4 μm wavelength as a function of QW thickness and indium (In) composition. Different recombination mechanisms were analyzed as a function of tensile strain in ϵ-Ge QW. Minority carrier lifetime and band alignment are key attributes of a QW laser, which were measured using microwave photoconductive decay and X-ray photoelectron spectroscopy (as a function of In composition), respectively. The transition point of Ge to a direct bandgap material is re-affirmed to be at ϵ = 1.6% (In ∼24%) and the transition from type I to type II for ϵ-Ge/InxGa1-xAs QW is found to be at In ∼55%. Also, the transition to a TM mode dominant laser is identified at In ∼15%. Using a tunable waveguide design to optimize confinement as a function of In composition, strain, wavelength, QW thickness, refractive index, and geometry, the ϵ-Ge QW laser design provided a net material gain of ∼2000 cm−1 and a threshold current density of ∼5 kA/cm2, which is an improvement over existing Ge based lasers. The impact of In composition and QW thickness on the band structure, polarized gain spectra, and various lasing metrics were analyzed to show ϵ-Ge/InGaAs QW lasers as promising for integrated photonics.

The implantation and rapid thermal annealing of sulfur (S+) ions has previously been shown to be an effective method in non-epitaxially attaining hole carrier concentrations as high as $1\times {10^{19}} \; \rm cm^{-3}$ in gallium antimonide (GaSb). This technique was used to fabricate a photovoltaic diode by delta-doping the front surface of a p-type GaSb substrate and forming a p++/p junction. The steep potential created using this process is increased by strong Fermi level pinning at the metal/p++ interface, resulting in a camel diode with a barrier height of 0.51 eV. A post-fabrication etch process succeeded in improving the short circuit current density to 41.8 mA/cm$^2$ and the internal quantum efficiency to 90% by enhancing the carrier lifetime away from the front metal contact grid. Likewise, the open circuit voltage improved to 0.21 V, with an intrinsic fill factor above 40%. These results offer the potential of a significantly higher power output than similar non-epitaxial devices made on n-type GaSb substrates.