Research Toward a Heterogeneously Integrated InGaN Laser on Silicon

Abstract

A heterogeneously integrated InGaN laser diode (LD) on Si is proposed as a path toward visible wavelength photonic integrated circuits (PICs) on Si. Herein, InGaN films are vertically stacked on a TiO2 waveguide (WG) fabricated on a Si wafer by bonding. In the light propagation direction, it is composed of a hybrid InGaN/TiO2 section, a TiO2 WG, an adiabatic taper, and mirrors that can form a cavity. As the refractive index of GaN is well matched with that of TiO2, the optical transverse mode extends to both the GaN and TiO2 in a hybrid mode. Modes between a hybrid InGaN/TiO2 and a pure TiO2 WG can transfer with an adiabatic taper structure. The coupling loss is calculated to be less than 0.5 dB with fairly short taper length of 78 μm and tip width of 200 nm. GaN substrate removal and bonding are critical fabrication steps of this LD and PIC. The substrate removal is successfully done by photoelectrochemical etching. Although direct bonding of GaN wafers with thermal oxide on Si is successful, GaN epitaxial wafers are more difficult. An implication and remedy of this is discussed in terms of surface roughness of GaN epitaxial film.

High-Performance Silicon Photonics Using Heterogeneous Integration

“…While most of the contents covered in this paper is about heterogeneous integration for O-band and C-band applications, it is important to note that heterogeneous integrated silicon photonics is also playing an important role in applications for extended wavelength ranges, including visible, mid-infrared (mid-IR) and so on [90]- [93]. For visible applications, InGaN-based gain materials can be integrated with TiO 2 or SiN waveguides on Si, as the optical refractive index (InGaN and TiO 2 ) are similar to facilitate efficient evanescent coupling between the active and passive sections [94]. High-Q SiN resonators have been demonstrated in the blue and violet regions [95], and self-injection locked InGaN lasers to these resonators should revolutionize the performance of visible lasers for a variety of display, sensor and optical clock applications.…”

Semipolar {202¯1} GaN Edge-Emitting Laser Diode on Epitaxial Lateral Overgrown Wing

“…Briefly, the process by which we may lower the commercialization hurdle consists of (1) utilizing ELO on expensive, free-standing GaN substrates for optical device fabrication, (2) removing the devices from the substrate, and (3) reusing the expensive substrate. This procedure of removing GaN thin films can also be beneficial in the bonding and integration of visible wavelength devices onto the Si photonics platform [29]. While earlier work reported a functional {1010}-non-polar LD with a laser ridge on an ELO open window [21], non-polar crystalline planes limit the attainable indium content.…”

Single-Crystalline All-Oxide α–γ–β Heterostructures for Deep-Ultraviolet Photodetection

“…Undeniably, such a platform would also allow the direct growth of conventional group-III-V-based light-emitting devices without the need for tedious photoelectrochemical etching for substrate removal and wafer bonding as in the case of heterogeneous integration on silicon-based platforms. 27,28 The eventual realization of a transparent all-oxide-based photonic platform would find promising applications in nextgeneration augmented-reality displays, smart goggles, smart windows, head-up displays, and other see-through devices. [29][30][31] This would be the case particularly where large-bandgap DUV photodetectors could be integrated as monitoring sensors for harmful ultraviolet-C (UVC) radiation (i.e., wavelengths of 100-280 nm) coming from flames and other man-made sources (e.g., mercury lamps, welding torches, disinfection lamps), while maintaining high transparency across the visible wavelength region.…”

“…Recently, oxide-based photonic platforms relying on aluminum oxide (Al 2 O 3 ), with an ultra-large optical band gap of up to ∼7.6 eV, have attracted considerable attention as paradigm-shifting platforms for various transparent optoelectronic devices. − The realization of low-loss Al 2 O 3 waveguides, with an extended wavelength of up to 220 nm and substantially lower transmission losses compared to silicon nitride (Si 3 N 4 )-based waveguides, , is highly encouraging and paves the way for an integrated transparent oxide-based photonic platform across the visible wavelength region. Undeniably, such a platform would also allow the direct growth of conventional group-III–V-based light-emitting devices without the need for tedious photoelectrochemical etching for substrate removal and wafer bonding as in the case of heterogeneous integration on silicon-based platforms. , The eventual realization of a transparent all-oxide-based photonic platform would find promising applications in next-generation augmented-reality displays, smart goggles, smart windows, head-up displays, and other see-through devices. − This would be the case particularly where large-band-gap DUV photodetectors could be integrated as monitoring sensors for harmful ultraviolet-C (UVC) radiation (i.e., wavelengths of 100–280 nm) coming from flames and other man-made sources (e.g., mercury lamps, welding torches, and disinfection lamps), while maintaining high transparency across the visible wavelength region.…”