Periodic Reporting for period 2 - Opto silicon (Towards optical communication on silicon chips)
Période du rapport: 2022-05-01 au 2023-10-31
Our vision is to integrate light-emitting devices, based on hexagonal silicon-germanium (Hex-SiGe), with existing Si electronics and passive Si-photonics circuitry. This establishes a silicon-compatible technology platform, with full opto-electronic functionality. This new technology promises strongly improved performance in computing and sensing, while simultaneously reducing cost by mass production in existing silicon foundries.
Silicon dominates the electronics industry for more than half a century. However, with their standard cubic-diamond crystal structure silicon, germanium and SiGe-alloys are all indirect band gap semiconductors. Their inability to efficiently emit light has adversely shaped the semiconductor industry we know today. It subdivided the industry into an electronics industry based on silicon and a communication industry established on III/V semiconductor light sources. While III-V technology is lacking advanced electronic processing capabilities on-chip, the Si-electronics industry is severely lacking a light source for data transfer and communication. Accordingly, achieving efficient light emission from SiGe has been a holy grail in silicon technology for decades.
The hexagonal crystal polytype SiGe (Hex-SiGe), as pioneered by the project members, recently emerged as a new direct bandgap semiconductor with excellent light emission capabilities as shown in our Nature paper (Nature 580, 205–209 (2020)). Hex-SiGe is therefore the essential brick that was missing in the silicon industry for opto-electronics capabilities. It will provide additional functionality like light generation (light emitting diode, laser), light amplification (semiconductor optical amplifier) and efficient light detection to silicon technology. These opto-electronic functionalities will expand Si-technology with novel possibilities like intra and inter-chip photonics networks. Last but not least, the fabrication of opto-electronic components in high volume silicon foundries will significantly reduce fabrication cost compared to existing solutions based on expensive III-V materials. By doing so, Hex-SiGe technology will be highly disruptive for both the existing electronics and the integrated photonics industry, since it has the potential to seamlessly merge them into a new SiGe-based opto-electronics industry.
Silicon dominates the electronics industry for more than half a century. However, with their standard cubic-diamond crystal structure silicon, germanium and SiGe-alloys are all indirect band gap semiconductors. Their inability to efficiently emit light has adversely shaped the semiconductor industry we know today. It subdivided the industry into an electronics industry based on silicon and a communication industry established on III/V semiconductor light sources. While III-V technology is lacking advanced electronic processing capabilities on-chip, the Si-electronics industry is severely lacking a light source for data transfer and communication. Accordingly, achieving efficient light emission from SiGe has been a holy grail in silicon technology for decades.
The hexagonal crystal polytype SiGe (Hex-SiGe), as pioneered by the project members, recently emerged as a new direct bandgap semiconductor with excellent light emission capabilities as shown in our Nature paper (Nature 580, 205–209 (2020)). Hex-SiGe is therefore the essential brick that was missing in the silicon industry for opto-electronics capabilities. It will provide additional functionality like light generation (light emitting diode, laser), light amplification (semiconductor optical amplifier) and efficient light detection to silicon technology. These opto-electronic functionalities will expand Si-technology with novel possibilities like intra and inter-chip photonics networks. Last but not least, the fabrication of opto-electronic components in high volume silicon foundries will significantly reduce fabrication cost compared to existing solutions based on expensive III-V materials. By doing so, Hex-SiGe technology will be highly disruptive for both the existing electronics and the integrated photonics industry, since it has the potential to seamlessly merge them into a new SiGe-based opto-electronics industry.
Workpackage 1: Preparation of hex-SiGe: Towards device quality
Demonstration of ohmic contacts to a hex-SiGe nanowire.
Measurements of the carrier concentration and the mobility by Shubnikov-de-Haas oscillations in hex-SiGe.
Lasher-Stern-Würfel fits indicate that the activated donor density has been reduced by a factor 10 down to 3.1017/cm3.
Workpackage 2: Growth of hex-SiGe on Si
Selective epitaxy in trenches incorporating hex-GaAs nanowires, which provides a route towards the fabrication of planar Hex-Ge films on Si.
Transformation of segments of cubic-Ge nanowires into hex-Ge. This is a first step towards a CMOS compatible fabrication route.
We have grown small parts of planar hex-SiGe on nearly lattice matched wurtzite CdS and ZnS substrates.
Workpackage 3: Demonstrate opto-electronic functionalities in hex-SiGe
Calculation of the band offsets and the confinement energies in m-plane hex-Ge/SiGe quantum wells. Observation of type I band alignment.
We has grown hex-Ge/SiGe quantum wells and demonstrated sharp interfaces and clear observed carrier confinement effects.
Observation of nanosecond radiative lifetime in hex-SiGe nanowire quantum wells.
We measured the tuning range of hex-SiGe alloys and found that the emission wavelength can be tuned down to 1.55µm at 4K (which was 1.8 µm before).
Workpackage 4: Strained quantum well laser on Si
We observed a super linear increase of confined modes inside a suspended nanowire, allowing to publish the observation of stimulated emission.
We observed an optical gain of 200 cm-1 in hex-SiGe.
We measured the carrier cooling dynamics in hex-SiGe which is lacking the polar optical phonon interaction. The carrier cooling time in hex-SiGe is comparable to an InGaAs/InP laser structure.
Demonstration of ohmic contacts to a hex-SiGe nanowire.
Measurements of the carrier concentration and the mobility by Shubnikov-de-Haas oscillations in hex-SiGe.
Lasher-Stern-Würfel fits indicate that the activated donor density has been reduced by a factor 10 down to 3.1017/cm3.
Workpackage 2: Growth of hex-SiGe on Si
Selective epitaxy in trenches incorporating hex-GaAs nanowires, which provides a route towards the fabrication of planar Hex-Ge films on Si.
Transformation of segments of cubic-Ge nanowires into hex-Ge. This is a first step towards a CMOS compatible fabrication route.
We have grown small parts of planar hex-SiGe on nearly lattice matched wurtzite CdS and ZnS substrates.
Workpackage 3: Demonstrate opto-electronic functionalities in hex-SiGe
Calculation of the band offsets and the confinement energies in m-plane hex-Ge/SiGe quantum wells. Observation of type I band alignment.
We has grown hex-Ge/SiGe quantum wells and demonstrated sharp interfaces and clear observed carrier confinement effects.
Observation of nanosecond radiative lifetime in hex-SiGe nanowire quantum wells.
We measured the tuning range of hex-SiGe alloys and found that the emission wavelength can be tuned down to 1.55µm at 4K (which was 1.8 µm before).
Workpackage 4: Strained quantum well laser on Si
We observed a super linear increase of confined modes inside a suspended nanowire, allowing to publish the observation of stimulated emission.
We observed an optical gain of 200 cm-1 in hex-SiGe.
We measured the carrier cooling dynamics in hex-SiGe which is lacking the polar optical phonon interaction. The carrier cooling time in hex-SiGe is comparable to an InGaAs/InP laser structure.
Hex-SiGe promises to combine the advantages of both Si-technology and III/V semiconductor technology by adding lasers and optical amplifiers to Si-photonics. This project will be foundational for:
• High performance energy efficient computing: A Hex-SiGe based photonic network-on-chip (PNoC) will significantly contribute to green ICT by reducing energy consumption by a factor 100 compared to current best technologies. A Hex-SiGe based PNoC employing passive Si-photonics circuitry will provide a high capacity network, potentially capable to operate at speeds of multiple Terabits/sec, as required for the most demanding high performance computing (HPC) applications.
• Low-cost disposable and implantable sensors: The emission wavelength of Hex-SiGe is tunable in the mid infrared between 1.8-4.2 µm, and can potentially be expanded to at least 6 µm by employing strained Hex-SiGe quantum well lasers to be developed in this project. This tuning window contains many strong vibrational transitions allowing Hex-SiGe sources to operate for sensing in the molecular fingerprint regime. Hex-SiGe lab-on-chip devices have potential applications for (implantable) biomedical sensors, pollution sensing, gas sensing or drug sensing. With this new technology mass-production of disposable or implantable sensors in Si-foundries will become a reality.
• Integrated LiDAR at low cost: LiDAR devices are of importance for the automotive industry developing self-driving cars. A LiDAR device can be integrated in Si-photonics, using a hybrid integrated III/V laser. A LiDAR sensor using a Hex-SiGe laser with a wavelength of 1800 nm is eye-safe and has good transmission through a foggy atmosphere, thus potentially providing a cost effective integrated LiDAR device for a very big market.
• Reduced energy consumption: Electrical data transfer within a chip is slow and energy inefficient. As an example, a 1 mm length metal interconnecting wire within a chip dissipates 100 fJ per bit, which adds up to an intolerable 100W dissipation at a data transfer rate of 1 petabit/s. Hex-SiGe on silicon allows to replace electrical connections by optical chiplet-chiplet or core-core communication within e.g. advanced microprocessors or graphical processing units (GPUs). Optical modulation has been reported at an energy per bit of <1fJ, thus >100x reducing the overall energy consumption for data transfer across 1 mm. It is important to stress that a tight integration of the different components on chip is expected to reduce stray capacitances and potentially provides a route to reduce energy consumption down into the attoJoule/bit level. Tight integration requires a monolithic integration approach to which Hex-SiGe is key!
• Environmental protection: As compared to typical light emitting III/V semiconductors, which contain toxic compounds including arsenides and rare heavy metals like indium, our intended technology uses silicon or SOI substrates requiring only abundant elements. Silicon is a nontoxic semiconductor while germanium has a low toxicity which will support the next generation of products that must be designed in a sustainable fashion and to minimize adverse environmental impact on our society.
• High performance energy efficient computing: A Hex-SiGe based photonic network-on-chip (PNoC) will significantly contribute to green ICT by reducing energy consumption by a factor 100 compared to current best technologies. A Hex-SiGe based PNoC employing passive Si-photonics circuitry will provide a high capacity network, potentially capable to operate at speeds of multiple Terabits/sec, as required for the most demanding high performance computing (HPC) applications.
• Low-cost disposable and implantable sensors: The emission wavelength of Hex-SiGe is tunable in the mid infrared between 1.8-4.2 µm, and can potentially be expanded to at least 6 µm by employing strained Hex-SiGe quantum well lasers to be developed in this project. This tuning window contains many strong vibrational transitions allowing Hex-SiGe sources to operate for sensing in the molecular fingerprint regime. Hex-SiGe lab-on-chip devices have potential applications for (implantable) biomedical sensors, pollution sensing, gas sensing or drug sensing. With this new technology mass-production of disposable or implantable sensors in Si-foundries will become a reality.
• Integrated LiDAR at low cost: LiDAR devices are of importance for the automotive industry developing self-driving cars. A LiDAR device can be integrated in Si-photonics, using a hybrid integrated III/V laser. A LiDAR sensor using a Hex-SiGe laser with a wavelength of 1800 nm is eye-safe and has good transmission through a foggy atmosphere, thus potentially providing a cost effective integrated LiDAR device for a very big market.
• Reduced energy consumption: Electrical data transfer within a chip is slow and energy inefficient. As an example, a 1 mm length metal interconnecting wire within a chip dissipates 100 fJ per bit, which adds up to an intolerable 100W dissipation at a data transfer rate of 1 petabit/s. Hex-SiGe on silicon allows to replace electrical connections by optical chiplet-chiplet or core-core communication within e.g. advanced microprocessors or graphical processing units (GPUs). Optical modulation has been reported at an energy per bit of <1fJ, thus >100x reducing the overall energy consumption for data transfer across 1 mm. It is important to stress that a tight integration of the different components on chip is expected to reduce stray capacitances and potentially provides a route to reduce energy consumption down into the attoJoule/bit level. Tight integration requires a monolithic integration approach to which Hex-SiGe is key!
• Environmental protection: As compared to typical light emitting III/V semiconductors, which contain toxic compounds including arsenides and rare heavy metals like indium, our intended technology uses silicon or SOI substrates requiring only abundant elements. Silicon is a nontoxic semiconductor while germanium has a low toxicity which will support the next generation of products that must be designed in a sustainable fashion and to minimize adverse environmental impact on our society.