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Active-passive GaN Scheme Shows Promise for Photonic Integration

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Researchers from Nanjing University have proposed an active-passive photonic integration scheme that showcases a photonic integrated circuit chip that combines a light source, modulator, photodiode, waveguide, and Y-branch splitter, all based on a gallium-nitride (GaN)-on-silicon platform. What sets this approach apart, according to its developers, is that all active devices, including the light source, modulator, and photodiode, are built on the same ultraviolet InGaN/AlGaN multiple quantum-well (MQW) structure. This significantly reduces fabrication complexity and cost, they said.

InP-based photonic integration is recognized as a reliable and comprehensive active-passive platform, though it has limitations in terms of yield and substrate size. Monolithic silicon photonics, on the other hand, boast excellent passive performance, temperature-intensive modulators, and compatibility with complementary metal oxide semiconductor (CMOS) fabrication. Yet, the lack of a light source has so far hindered the development of this technology.
Photonic integration with active–passive functions based on GaN-on-silicon platform. Courtesy of Jiabin Yan, Nanjing University of Posts and Telecommunications.
Photonic integration with active-passive functions based on GaN-on-silicon platform. Courtesy of Jiabin Yan, Nanjing University of Posts and Telecommunications.

The researchers designed their circuit chip based on the GaN-on-silicon platform and using III-nitride epitaxial layers grown through metal organic chemical vapor deposition. The monolithic, top-down approach builds III-nitride transmitters, modulators, waveguides, beamsplitters, receivers, and monitors on a conventional GaN-on-silicon wafer and does not involve regrowth or postgrowth doping.


The researchers characterized the resulting chip extensively from various perspectives to validate the effectiveness of this innovative photonic integration scheme. Results indicated that a higher reverse bias voltage applied to the modulator led to increased light absorption, as caused by changes in the absorption coefficient. The distinctive modulation effect was reflected in the receiver’s photocurrent changes. The test system demonstrated negligible cross-talk and the isolation between the light source and modulator on the same waveguide, achieved through p-contact layer separation, proved sufficient for optimal system performance.

By employing direct and indirect modulations within a single light path, the researchers simultaneously transmitted two types of data or encrypted one modulation signal’s data transmission with another modulation.

The researchers’ results further validated the data transmission and processing using UV light with a peak emission wavelength of 386 nm, the researchers said. In addition, “The adoption of multifunction MQW completely overcomes the compatibility problem of different optical active devices and considerably reduces fabrication complexity,” they said.

According to research team leader and senior corresponding author Yongjin Wang of the Peter Grünberg Research Center at Nanjing University of Posts and Telecommunications, further advancements in III-nitride etching accuracy added to the proposed integration scheme hold high potential for next-generation photonic integration. Applications in the sensing field, where high integration density is not a critical requirement, Wang said, are especially promising.

The research was published in Advanced Photonics Nexus (www.doi.org/10.1117/1.APN.2.4.046003).


Published: June 2023
Glossary
substrate
A substrate refers to a material or surface upon which another material or process is applied or deposited. In various fields, such as electronics, biology, chemistry, and manufacturing, the term "substrate" is used with specific contexts, but the fundamental definition remains consistent: it is the underlying material or surface that provides a foundation for subsequent processes or applications. Here are some examples of how a substrate is used in different fields: Electronics: In...
light source
The generic term applied to all sources of visible radiation from burning matter to ionized vapors and lasers, regardless of the degree of excitation.
waveguide
A waveguide is a physical structure or device that is designed to confine and guide electromagnetic waves, such as radio waves, microwaves, or light waves. It is commonly used in communication systems, radar systems, and other applications where the controlled transmission of electromagnetic waves is crucial. The basic function of a waveguide is to provide a path for the propagation of electromagnetic waves while minimizing the loss of energy. Waveguides come in various shapes and sizes, and...
indium phosphide
Indium phosphide (InP) is a compound semiconductor material composed of indium (In) and phosphorus (P). It belongs to the III-V group of semiconductors, where elements from groups III and V of the periodic table combine to form a variety of important semiconductor materials. Indium phosphide is known for its favorable electronic and optical properties, making it widely used in the fabrication of optoelectronic devices. Key features and properties of indium phosphide include: Bandgap:...
gallium nitride
Gallium nitride (GaN) is a compound made up of gallium (Ga) and nitrogen (N). It is a wide-bandgap semiconductor material that exhibits unique electrical and optical properties. Gallium nitride is widely used in the production of various electronic and optoelectronic devices, including light-emitting diodes (LEDs), laser diodes, power electronics, and high-frequency communication devices. Key points about gallium nitride (GaN): Chemical composition: Gallium nitride is a binary compound...
Research & Technologyphotonic integrated circuitsPICphotonic integrationMaterialssubstratelight sourceLasersOpticsWaveguideindium phosphideInPgallium nitridesiliconNanjing University of Posts and TelecommunicationsNanjing UniversityAsia-PacificTechnology News

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