In the present talk we discuss the application of Template-Assisted Selective Epitaxy (TASE) for the monolithic integration of III-V active photonic devices on silicon. The main concept of TASE relies on the guided growth of III-Vs within a confined oxide template. At one extremity of the template there is access to silicon to start the nucleation, and subsequently it is the template which guides the growth progression. This decoupling of the resulting geometry from the growth mode and substrate orientation, results in a larger processing window as we no longer rely on the growth conditions to tune the geometry, as well as a number of other advantages. A further unique advantage of TASE for silicon photonics applications is that it allows for the truly local integration of III-V material at precisely defined positions, since the location of the III-V may be defined with nm-scale precision in the same lithographic step as silicon passives. TASE was originally developed for electronics, but in recent years we have expanded it to enable several photonic devices. In the present talk, I will discuss our work on GaAs and InP microdisk lasers fabricated by either direct growth or via the use of micro-substrates. These devices show lasing at room temperature around 870 nm with thresholds of about 10 pJ/pulse. We also explore the use of metal-clad cavities for further light confinement.
Hexagonal SiGe has been theoretically shown to feature a tunable direct bandgap in the range 0.4-0.8eV. We study arrays of site-selectively grown Si_(1-x)-Ge_x nanowires (NWs) grown using the crystal transfer method in which wurtzite GaP core NWs are used as template for SiGe growth. Our approach opens up routes towards photonic band-edge lasers using group-IV NWs. Low-temperature µPL studies of arrays of SiGe NW-arrays reveal strong emission at 0.395eV and linear power dependence for weak excitation levels (P_ex~0.01-1kW/cm^2). For P_ex>4kW/cm^2, a new peak emerges at 0.37eV with an intensity that increases according to ~(P_ex)^5, indicative of stimulated emission close to the photonic band-edge.
As performance and power consumption of modern micro-chips are increasingly limited by electrical on-chip interconnects, all-optical interconnect systems promise data transmission at speed of light and wavelength- division multiplexing. To realize complex networks, active devices, like lasers, need to be integrated on Si. III-Vs are excellent candidates for optical devices, however, their integration on Si is challenging due to a significant lattice and thermal mismatch. Template-assisted selective epitaxy (TASE) was recently developed by our group, allowing for the selective growth of III-Vs from a small Si seed in a confined oxide template. In this work, we extend TASE towards optical devices and demonstrate the monolithic integration of InGaAs lasers via a novel approach using a virtual substrate (VS) in a two-step templated growth. First, μm2 sized 60 nm thick InGaAs VSs are grown by MOCVD using TASE on SOI. Subsequently, 500 nm oxide are deposited onto the VS and patterned in arbitrary shapes like disks, and rings. In a second InGaAs growth, the defined vertical cavities are filled. The investigated structures have diameters of 1.7 μm, thicknesses of 0.5 µm and total cavity volumes of 0.5 λ30. Photoluminescence spectroscopy reveals a broad spontaneous emission peak around 1.1 μm (FWHM = 150 nm) that increases linearly with pump power for low excitation powers (<< 2.6 pJ/pulse). Above excitation threshold, a strong emission peak emerges at 1.1 μm (FWHM = 7 nm). The Input-Output curve (log- log, T = 10 K) exhibits the characteristic S-shape which constitutes a strong indication for the lasing operation. The onset of the lasing threshold is observed up to 200 K with a characteristic temperature of T0 = 192 K.
We will present our recent work on III-V micro-cavity lasers monolithically grown on silicon substrates. The III-V material is directly grown using Template-Assisted-Selective-Epitaxy (TASE) within oxide cavities patterned using conventional lithographic techniques on top of the silicon substrate. This allows for the local integration of single-crystal III-V active gain material. Two variations of this technique will be discussed; the direct growth of disc lasers and the two-step approach via a virtual substrate. Room temperature single-mode optically pumped lasing is achieved in GaAs micro-cavity lasers, and devices show a remarkably low shift of the lasing threshold (T0=170K) with temperature. Dependence on cavity geometry and pump power will be discussed.
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