The first ultra-low threshold continuous wave generation in GeSn

Scanning electron micrographs: (left) The GeSn layer is transferred onto a silicon substrate and then structured as a microdisk to form an optical resonator. During transfer, the defective layer in GeSn, which was at the interface with the Ge / Si substrate, was removed by etching. The transfer also allows you to insert a stressed SiNx layer under the GeSn layer. An aluminum layer was used to maintain the cavity, allowing excellent thermal cooling of the laser device through the substrate. (right) The final conformal deposition of a deformed film onto a microdisk allows one to obtain a “comprehensive” configuration of voltage transfer from SiNx to GeSn. Then GeSn experiences a tensile strain of 1.6%, very evenly distributed in its active volume. Courtesy: C2N / M. El Kurdi & al.

Transistors in computer chips work electrically, but data can be transmitted faster with light. Therefore, researchers have long been looking for a way to integrate the laser directly into silicon chips. A team of physicists from the Center for Nanotechnology and Nanotechnology, in collaboration with researchers from Forschungszentrum Jülich (FZJ) and STMicroelectronics of Germany, has introduced a new method for constructing materials for the manufacture of laser microdiscs in stressed germanium-tin (GeSn). ) alloy. They demonstrated a laser device with a Group IV compound compatible with silicon, operating at an ultra-low threshold and with continuous excitation.

Optical data transfer provides significantly higher data rates and ranges than conventional electronic processes, while using less energy. Therefore, in data centers, optical cables about 1 meter long are standard. In the future, optical solutions will be required for shorter distances to transfer data from board to board or from chip to chip. Pumped Electric laser which is compatible with silicon-based CMOS technology, would be ideal for achieving very high data rates.

GeSn alloys promising for the implementation of light emitters, such as lasers. Based solely on Group IV semiconductor elements, this alloy is silicon compatible and can be fully integrated into the CMOS manufacturing chain, which is widely used to manufacture electronic chips for basic applications. Today, the main approach is to introduce as much tin as possible into the GeSn alloy (in the range of 10-16%). Thus, the resulting compound provides a direct alignment of the band structure, which provides laser radiation. However, this approach has significant drawbacks: due to the lattice mismatch between the germanium (stress-relaxed) silicon substrate and GeSn alloys with a high tin content, a very dense network of dislocation defects is formed at the interface. Thus, an extremely high energy density (hundreds of kW / cm) is required.2 at cryogenic temperature) to achieve laser radiation.

Using a different approach based on a specific technology of materials, physicists received laser radiation in a microdisk from a GeSn alloy, completely encapsulated by a layer of a stressor made of silicon nitride (SiN) dielectric.X) Using this device, they first demonstrated laser radiation in an alloy capable of operating under continuous (continuous) excitation. The laser effect is achieved with continuous and pulsed excitation with ultra-low thresholds compared to the state of the art. Their results are published in Photonics of nature,

This device uses a 300 nm thick GeSn layer with a tin content of only 5.4%, encapsulated SiN.X stressor layer to obtain tensile deformation of the lattice. The layer of the grown alloy is initially an indirect band gap semiconductor that does not support the laser effect and is a very poor emitter. Researchers show that it can be converted into a truly direct forbidden semiconductor, which can support the laser effect and, thus, becomes an effective emitter by applying tensile deformation to it. In addition, tensile strain provides a low density of states at the edge of the valence band, which is a strip of light holes, which reduces the required level of excitation to achieve laser action. Due to its low tin concentration, the dislocation network is less dense and easier to process. The special design of the microdisk cavity was developed to ensure high transfer of deformation from the stressor layer to the active region, eliminate interface defects and improved thermal cooling of the active region.

Using this device, researchers for the first time demonstrate continuous (continuous) generation up to 70 K, while pulsed generation is achieved at temperatures up to 100 K. Lasers operating at a wavelength of 2.5 μm have ultra-low thresholds of 0.8. kW / cm2 for nanosecond pulsed optical excitation and 1.1 kW / cm2 with continuous optical excitation. Since these threshold values ​​are 2 orders of magnitude lower than reported in the literature, the results open up a new path to the integration of a Group IV laser on a Si-photon platform.

Researchers Improve Silicon Semiconductor Laser

Additional Information:
Anas Elbaz et al. Ultra-low threshold continuous and pulsed generation in tensile deformed GeSn alloys, Photonics of nature (2020). DOI: 10.1038 / s41566-020-0601-5

First ultra-low threshold continuous generation at GeSn (2020, March 20)
retrieved March 21, 2020

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