Periodic Reporting for period 1 - REGEN-PE (Recyclable Energy-Efficient Rare-Earth Nitrides Power Electronics)
Período documentado: 2024-09-16 hasta 2026-09-15
Transmission and distribution losses in electric energy account for about 10% of total production in developed countries. The majority of these losses stem from semiconductor devices used in power transformation. With silicon nearing its physical limitations, wide bandgap (WBG) semiconductors, displaying superior properties, are being embraced to enhance efficiency. Currently, SiC is well-established, and GaN-based high electron mobility transistors (HEMTs) are entering the market.
Going even further, incorporating rare-earth metals into AlN enhances its polarization effects. This advancement enables the further enhancement of GaN-based HEMTs performances by engineering heterostructures with a higher density of polarization charges. Moreover, they provide the opportunity to grow lattice-matched layers on GaN, making them even more appealing. Such structures eliminate the challenges of high thermal and lattice mismatch, preventing the formation of dislocations or cracking due to strain relaxation. The most extensively studied is ScAlN, which has captured significant interest from the nitride community due to its intriguing ferroelectric and piezoelectric properties. Recently, a lattice-matched ScAlN/GaN heterostructure with an electron sheet concentration about five times larger than conventional metal-polar AlGaN/GaN structures used in HEMTs was demonstrated. These structures hold promise for multichannel heterostructure power devices, offering increased charge densities per channel and unlimited stacking potential due to lattice-match growth. With the potential to exceed the theoretical performance limit of GaN, these devices hold great promise for power electronics conversion, with heat extraction being the ultimate performance constraint.
However, despite the considerable potential of ScAlN, its practical applications are hindered by the high cost of scandium, thereby diminishing its attractiveness. Yttrium, on the other hand, offers a more abundant and cost-effective alternative with a similar electronic outer shell configuration to scandium. When alloyed with AlN materials, yttrium is capable of exhibiting similar properties. In fact, YAlN could offer several key advantages: It exhibits greater stability in the wurtzite phase with Y content up to 75% and requires a lower concentration to achieve lattice-match with GaN. However, while this material has been recently synthesized by metal organic chemical vapor deposition (MOCVD), its properties are still not fully understood, and the growth of YAlN is not fully mastered. Even so, a recent demonstration of an YAlN/AlN/GaN heterojunction-based HEMT highlighted its tremendous potential, with high mobility and similar sheet carrier concentration as its scandium counterpart.
Moreover, in the last five years, global consumption of Ga has quadrupled, resulting in potential long-term supply vulnerabilities, while the recycling rate of Ga within components remains negligible. This situation poses a challenge for the sustainable integration of III-N electronics into mass production. However, there are minimal research efforts dedicated to addressing this problem and advancing towards a circular engineering model. One potential solution for recycle nitride electronics involves laser ablation to extract the active regions from the substrate templates, followed by vacuum sublimation of the GaN/AlN layers. This process has the potential to induce phase separation of the three elements involved: solid Al, liquid Ga, and gaseous N. Additionally, the inclusion of group-III transition metals can facilitate this process by reducing the sublimation temperature, thereby lowering the cost of the operation. However, despite the relative simplicity of the process, there is currently no available literature on this topic, highlighting the need for dedicated research with significant potential impact.
This project is driven by the vision to revolutionize power electronics by developing high-quality novel nitride layers that not only enable affordable ultra-efficient performance but also promote sustainability through recycling. To achieve this ambitious goal, we adopt an ambitious approach that combines material density functional theory (DFT) simulations, sputtering and MOCVD for epitaxy, along with chemical and optical characterization techniques for material development. The project includes the successful integration of novel rare-earth nitrides into cutting-edge electronic device structures, projected to surpass the GaN performance limit, which requires their design, fabrication, and electrical characterization. However, what sets the REGEN-PE project apart is its unwavering commitment to sustainability. By developing a novel method for material recovery, we aim to establish a precedent for recyclable semiconductor technology. REGEN-PE promotes a circular engineering approach, which sets the stage for the future of high-performance green power electronics.
Objectives
O1: Predict new rare-earth nitrides bulk and interfacial properties using DFT calculations.
O2: Grow high-quality lattice-matched new rare-earth nitrides on GaN
O3: Demonstrate a high-performance new rare-earth nitrides based transistor
O4: Develop a recycling process for nitride-based components.
Going even further, incorporating rare-earth metals into AlN enhances its polarization effects. This advancement enables the further enhancement of GaN-based HEMTs performances by engineering heterostructures with a higher density of polarization charges. Moreover, they provide the opportunity to grow lattice-matched layers on GaN, making them even more appealing. Such structures eliminate the challenges of high thermal and lattice mismatch, preventing the formation of dislocations or cracking due to strain relaxation. The most extensively studied is ScAlN, which has captured significant interest from the nitride community due to its intriguing ferroelectric and piezoelectric properties. Recently, a lattice-matched ScAlN/GaN heterostructure with an electron sheet concentration about five times larger than conventional metal-polar AlGaN/GaN structures used in HEMTs was demonstrated. These structures hold promise for multichannel heterostructure power devices, offering increased charge densities per channel and unlimited stacking potential due to lattice-match growth. With the potential to exceed the theoretical performance limit of GaN, these devices hold great promise for power electronics conversion, with heat extraction being the ultimate performance constraint.
However, despite the considerable potential of ScAlN, its practical applications are hindered by the high cost of scandium, thereby diminishing its attractiveness. Yttrium, on the other hand, offers a more abundant and cost-effective alternative with a similar electronic outer shell configuration to scandium. When alloyed with AlN materials, yttrium is capable of exhibiting similar properties. In fact, YAlN could offer several key advantages: It exhibits greater stability in the wurtzite phase with Y content up to 75% and requires a lower concentration to achieve lattice-match with GaN. However, while this material has been recently synthesized by metal organic chemical vapor deposition (MOCVD), its properties are still not fully understood, and the growth of YAlN is not fully mastered. Even so, a recent demonstration of an YAlN/AlN/GaN heterojunction-based HEMT highlighted its tremendous potential, with high mobility and similar sheet carrier concentration as its scandium counterpart.
Moreover, in the last five years, global consumption of Ga has quadrupled, resulting in potential long-term supply vulnerabilities, while the recycling rate of Ga within components remains negligible. This situation poses a challenge for the sustainable integration of III-N electronics into mass production. However, there are minimal research efforts dedicated to addressing this problem and advancing towards a circular engineering model. One potential solution for recycle nitride electronics involves laser ablation to extract the active regions from the substrate templates, followed by vacuum sublimation of the GaN/AlN layers. This process has the potential to induce phase separation of the three elements involved: solid Al, liquid Ga, and gaseous N. Additionally, the inclusion of group-III transition metals can facilitate this process by reducing the sublimation temperature, thereby lowering the cost of the operation. However, despite the relative simplicity of the process, there is currently no available literature on this topic, highlighting the need for dedicated research with significant potential impact.
This project is driven by the vision to revolutionize power electronics by developing high-quality novel nitride layers that not only enable affordable ultra-efficient performance but also promote sustainability through recycling. To achieve this ambitious goal, we adopt an ambitious approach that combines material density functional theory (DFT) simulations, sputtering and MOCVD for epitaxy, along with chemical and optical characterization techniques for material development. The project includes the successful integration of novel rare-earth nitrides into cutting-edge electronic device structures, projected to surpass the GaN performance limit, which requires their design, fabrication, and electrical characterization. However, what sets the REGEN-PE project apart is its unwavering commitment to sustainability. By developing a novel method for material recovery, we aim to establish a precedent for recyclable semiconductor technology. REGEN-PE promotes a circular engineering approach, which sets the stage for the future of high-performance green power electronics.
Objectives
O1: Predict new rare-earth nitrides bulk and interfacial properties using DFT calculations.
O2: Grow high-quality lattice-matched new rare-earth nitrides on GaN
O3: Demonstrate a high-performance new rare-earth nitrides based transistor
O4: Develop a recycling process for nitride-based components.
Due to the shorter fellowship duration than initially planned, the project focused on the initial planned stage: The theoretical comprehension of the rare-earth nitrides and simulation of their properties. In particular, density functional theory was used to perform calculations of the electronic, elastic and polarization properties of mainly the forth-row rare-earth metal nitrides in their rocksalt, zincblende and wurtzite phases. Thanks to these simulations, two main results can be highlighted:
-The link between their elastic properties and density of states was understood for forth-row rare-earth metal nitrides within their rocksalt, zincblende and wurtzite phases. The density of states of the full set of forth-row rare-earth nitrides shares a very similar character and the variation of these materials’ stiffness can be understood via the filling of bonding/antibonding states as the fermi level rises due to the incorporation of heavier elements.
-The spontaneous polarization physical origin was theoretically understood, linked to ferroelectricity and decoupled from interface charges. The formal polarization of conventional nitrides was calculated via berry phase through structural transformations connecting the polarization of wurtzite, zincblende and rocksalt. This represents a great step forward in the physical comprehension of these quantities while also allowing the calculation of charge gradients in nitride interfaces.
-The link between their elastic properties and density of states was understood for forth-row rare-earth metal nitrides within their rocksalt, zincblende and wurtzite phases. The density of states of the full set of forth-row rare-earth nitrides shares a very similar character and the variation of these materials’ stiffness can be understood via the filling of bonding/antibonding states as the fermi level rises due to the incorporation of heavier elements.
-The spontaneous polarization physical origin was theoretically understood, linked to ferroelectricity and decoupled from interface charges. The formal polarization of conventional nitrides was calculated via berry phase through structural transformations connecting the polarization of wurtzite, zincblende and rocksalt. This represents a great step forward in the physical comprehension of these quantities while also allowing the calculation of charge gradients in nitride interfaces.
-The link between their elastic properties and density of states was understood for forth-row rare-earth metal nitrides within their rocksalt, zincblende and wurtzite phases. A consistent dataset for the elastic properties of these materials was generated. This will allow the identification of trends, and the screening of materials for specific applications. In particular, it will impact the future development of rare-earth nitrides that can be implemented within bulk acoustic wave components needed for the next generation of smartphones and devices. However, further research is needed to advance the understanding of piezoelectric constants and its trends within rare-earth nitrides and the effect of ternary alloys.
-The formal polarization of conventional nitrides was calculated via berry phase through structural transformations connecting the polarization of wurtzite, zincblende and rocksalt. This represents a step forward in the fundamental comprehension of the polarization in these materials. It allows the calculation of charge gradients in nitride interfaces of such phases. This will produce an impact on the design of new nitride electronic devices, leading to more efficient devices and energy-savings in the energy conversion in the future. Further experimental research is needed to confirm the theoretical predictions, together with the material developement needed to integrate these new nitrides within devices.
-The formal polarization of conventional nitrides was calculated via berry phase through structural transformations connecting the polarization of wurtzite, zincblende and rocksalt. This represents a step forward in the fundamental comprehension of the polarization in these materials. It allows the calculation of charge gradients in nitride interfaces of such phases. This will produce an impact on the design of new nitride electronic devices, leading to more efficient devices and energy-savings in the energy conversion in the future. Further experimental research is needed to confirm the theoretical predictions, together with the material developement needed to integrate these new nitrides within devices.