Integration Of III-V Materials Research Articles

Cu Nanoparticle Array-Mediated III–V/Si Integration: Application in Series-Connected Tandem Solar Cells

The integration of III-V materials with crystalline Si (c-Si) is a promising pathway to design high-performance optoelectronic devices, including solar cells. We have previously reported high-effic...

(Invited) Hybrid III-V/Si CMOS Technology Platform: From Materials for Logic to Integrated RF and Photonics

In the past few years, tremendous progress has been achieved in the integration of III-V compound semiconductors on a Si CMOS platform as high-mobility channel materials are foreseen as potential candidates to replace Si channels in advanced CMOS technology nodes. Beyond CMOS scaling, the integration of III-V materials and devices on a Si CMOS platform enables bringing their traditional enhanced functionalities to the chip level: high-speed low-noise RF as well as lasers and sensitive photodetectors. In this presentation, we will review the technologies that we developed to monolithically integrate III-V materials on Si by direct epitaxy in empty oxide cavities or by direct wafer bonding. We will show that record logic n-MOSFET performance can be achieved for ultra-scaled gate lengths (Lg = 13nm), that hybrid III-V/Si(Ge) CMOS functionality can be obtained (inverters, 6T-SRAMs). We will then highlight how 3D monolithic integration enables seamless integration of III-V functionalities on top of Si CMOS front-end for logic as well as for RF and Photonics.

Amplified Spontaneous Emission from Gesn Waveguides at Room Temperature

Silicon is the basis for a multibillion dollar industry and has been the preferred platform for integrated electronics for decades. Unfortunately, the band structure of Si has limited its use in infrared applications. The 1.12 eV band gap restricts the range of Si photodetectors to wavelengths of 1100 nm or lower, and the indirect nature of the band gap has prevented the realization of a Si-based laser. Although there are devices available that cover these wavelength ranges, they are typically made from exotic materials such as InGaAs or HgCdTe. These materials are incompatible with Si processing, so the device cannot be integrated with other Si-based electronics on the same chip. Furthermore, many of the devices require cryogenic temperature operation. These unfortunate conditions mean that the devices and systems that use them are prohibitively expensive, which prevents their widespread adoption for both military and commercial applications. Si-compatible materials that have desirable optical properties beyond the band gap of silicon could produce inexpensive devices and systems with applications in telecommunications, low-light imaging, targeting and acquisition, photonic integrated circuit. A number of approaches have been attempted for producing infrared devices on silicon, but they have achieved limited success. The integration of III-V materials on Si has been an active research area for a number of years, and it has yielded limited success. The flip chip wafer bonding and packaging process still requires a separate facility for production of the III-V material, so the costs cannot be brought down to the level that would be achieved with a Si-compatible material. Another approach has been to use other Group IV materials that are grown epitaxially on Si. SiGe alloys were explored for this purpose, but for the concentrations of Ge that can readily be achieved, the band gap still does not extend far enough into the infrared. Furthermore, SiGe is still an indirect band gap material, so it is not suitable for producing a laser. Pure Ge grown epitaxially on Si has also been a recent area of research, and this has resulted in some success. Detectors operating at 1550 nm have been achieved by using tensile strain to lower the direct band gap to enhance absorption at that wavelength, but this approach cannot be extended to further wavelengths due to the limits of achievable strain. Tensile-strained Ge has also been used to demonstrate optically- and electrically-pumped lasers. A new class of Group IV materials that are grown on Si or Ge-buffered Si is the GeSn alloy system. Pure Ge is an indirect band gap semiconductor, but the difference between the conduction band minima at the L- and Γ-points is only 140 meV. The diamond cubic structure of Sn, α-Sn, is a semimetal. When Sn is substituted for Ge in the Ge lattice, a hybrid band structure is formed, yielding a material with a tunable band gap. For Sn concentrations around 10% or lower, the band structure is still Ge-like with the lowest conduction band minimum at the L-point. However, the energy difference between the L- and Γ-minima reduces with increasing Sn concentration. For higher Sn concentrations, the minimum at the Γ-point becomes the lowest minimum, thereby creating a direct band gap semiconductor. In this talk, I will discuss our efforts to enhance optical emission in GeSn through the use of waveguide architectures and the introduction of n-type dopants. Our results obtained from optically-pumped waveguides indicate that we have achieved amplified spontaneous emission, where we see an exponential dependence of output power versus input power, but we do not see a narrowing of the optical emission spectrum. Instead, the entire spontaneous emission spectrum is amplified. This does produces some evolution in the spectrum, and we attempt to understand the emission spectrum through mathematical and physical modeling.

Progress in hybrid-silicon photonic integrated circuit technology

Progress in hybrid-silicon photonic integrated circuit technology Martijn J. R. Heck, Michael L. Davenport, and John E. Bowers Adding III-V materials to the silicon-on-insulator platform enables increasingly complex devices, making it well-positioned to address energy-efficient, compact, and low-cost photonic applications. Photonic integration is the technology that allows the combi- nation of different optical components, such as lasers, modula- tors, and photodetectors, on a single photonic chip. Such devices are known as photonic integrated circuits (PICs). The prospect of medium- and large-scale integration, with tens to hundreds of components on a single chip, is a major driver for research on silicon photonics in the silicon-on-insulator (SOI) platform. The SOI fabrication infrastructure is compatible with the mature and high-quality CMOS technology, which is robust and repro- ducible and has high yield. It is possible to make PICs in the SOI platform on large 200mm-diameter wafers, and this allows for low cost and high volumes. Since these PICs can operate at wavelengths of 1.3 and 1.55 m, prime application candidates are telecommunication and interconnects. 1 The SOI platform offers an almost complete suite of pho- tonic components, including filters, (de)multiplexers, splitters, modulators, and photodetectors. However, electrically pumped efficient sources on silicon remain a challenge due to this substance’s indirect bandgap. The integration of III-V materials, such as indium phosphide (InP), gives the SOI platform access to the complete suite of high-speed and efficient III-V-based photonic components. The hybrid-silicon complex heterogeneously incorporates III-V func- tionality on the SOI platform by means of molecular wafer bonding. 2 Hybrid-silicon III-V waveguides have the proper- ties of the III-V material, such as gain, high-speed modulation, and photodetection, but are still located on an SOI circuit (see Figure 1). We can use tapered-mode converters to change a hy- brid mode into a mode that resides fully in the silicon wave- guide. We can also fabricate the active III-V components with Figure 1. Diagram showing a hybrid-silicon III-V optical amplifier in- tegrated with a silicon waveguide (bottom) and the hybrid waveguide cross section (top). Tapered-mode converters form the interface between the silicon and hybrid waveguide. The optical mode (white) overlaps with both the silicon waveguide and the III-V quantum wells (red). The top p-contact and the lateral n-contacts (yellow) provide electrical current. The device achieves current confinement by ion implanting the p-mesa (dashed). SOI: Silicon on insulator. lithographic precision and alignment accuracy, thereby enabling large-scale integration. This is done in a back-end process af- ter the SOI fabrication, which means we avoid contamination of a CMOS foundry and that the III-V manufacturing is in prin- ciple fully compatible with the SOI-CMOS fabrication proce- dure. The hybrid-silicon platform combines the maturity and scale of CMOS processing and SOI photonics with essential III-V functionality and, as such, is unique and well-positioned for medium-scale photonic integration. The timeline of Figure 2 shows the success of the hybrid- silicon technology, which we developed in collaboration with Continued on next page

Far infrared photonic crystals operating in the Reststrahl region

We report here far infrared photonic crystals comprised of a lattice-matched pair of semiconductor materials: GaP and Si, or GaAs and Ge, or AlAs and GaAs. The crystals operate in a wavelength range where the real refractive index of one material undergoes a major dispersion associated with the LO and TO phonon absorption peaks. Using electromagnetic theory, we investigated the photonic-bandgap response for both TE and TM polarizations. Propagation losses for two types of crystals are estimated in this paper. These structures offer promise for the integration of III-V materials (GaP, GaAs) on group IV (Si, or Ge) for practical, active, far infrared photonic devices, such as light sources, amplifiers, modulators, reconfigurable waveguides and switches.