REWIRE’s Innovation Director Dr. Katie Hore and REWIRE academics from the Bristol Business School, Prof. Palie Smart and Dr. Minhao Zhang, discuss the importance of critical minerals, their role in the power semiconductor technologies, and insights about the impact of critical mineral supply chains and the need for resilience.
Critical minerals are those which are required for our economic success but whose supply chains are at significant risk of disruption. This has not escaped the attention of governments internationally and particularly the new presidency of Donald Trump and his administration. For example, his murmurings about the Arctic, Ukraine, and Congo have been described by some commentators as linked to the acquisition of rare earth and critical minerals. These materials are vital for the manufacturing of many electronic products upon which daily life depends– phones, cars, fridges, and national security. According to the Economist last month, the increase in renewables and electric cars will require vast amounts of critical materials over the next 20 years. The International Energy Agency estimates that annual demand for rare earths, nickel, cobalt, and lithium will grow by 62%, 73%, 80%, and 400%, respectively, by 2040. Furthermore, the demand for copper, which is already high, is projected to increase by one-third over the period to 37m tonnes.
Which minerals are deemed “critical” depends on who you ask: the UK (BGS, 2024) and the US (USGS, 2022), have critical minerals lists that are based on raw or refined elements. As of 2023, the US Geological Survey (USGS) lists 50 critical minerals, including rare earth elements, lithium, cobalt, and gallium (U.S. Geological Survey, 2022). The UK’s 2023 Critical Minerals Strategy identifies 18 minerals, prioritizing those crucial for clean energy and defence technologies (Deloitte, 2023). In contrast, Taiwan does not maintain a formal “critical minerals” list akin to those of the United States or the United Kingdom. Instead, its approach focuses on identifying supply-chain-critical products and functional materials, particularly those vital to its semiconductor and information and communication technology (ICT) sectors. Given its limited natural resources, Taiwan has become a leader in urban mining, reclaiming valuable materials from waste products and infrastructure. For instance, in 2022, Taiwan’s Solar Applied Materials Technology Corporation recycled 247 metric tons of materials, including gallium and indium, cutting carbon emissions by over 440,000 metric tons that year (Westcott, 2024). Regardless of these definitional nuances, recent restrictions on the export of certain critical minerals—particularly China’s 2023 export controls on gallium and germanium—have prompted governments worldwide to reassess, update, or develop their own critical minerals strategies. Essentially, a “critical mineral” is one whose supply is at risk of disruption and whose absence would have significant economic or strategic consequences.
Caption: Table identifying the critical minerals and their use across application categories as identified by the Critical Minerals Research Landscape Review. Many of these minerals are identified to be critical the electronics sector, and therefore by extension to the semiconductor sectors. Source – Critical Minerals Research Landscape Review, 2023.
Many of these minerals will be required in significant amounts for technologies that we are adopting in the transition to Net Zero. There has been plenty of focus on the mining and supply of lithium for electric vehicle batteries but there are many other components to an electric car and its charging system. For example, body panels made of aluminium, and semiconductor materials for the electronics.
Anyone who has kept an eye on critical mineral news will immediately recognise an element required in many semiconductor devices: gallium. Gallium is a soft, silvery-white metal from Group 13 of the periodic table, which is used in a new class of ‘compound’ semiconductors and is distinct from single-material semiconductors such as silicon. Compound semiconductors such as gallium nitride (GaN), gallium oxide (Ga2O3) and gallium arsenide (GaAs). GaN is replacing silicon in many power semiconductors, especially in cars. It has a wider band gap than silicon (3.4 eV vs 1.12 eV), which means that for the same voltage, a GaN device can be smaller than a silicon device. GaN semiconductor devices can turn on and off much faster than silicon, which, along with their smaller size, means lower losses and a more energy efficient device. GaN can also operate at higher temperatures than silicon, so temperature-related failures are reduced. Plus, GaN devices can achieve higher reliability and longer lifetimes, which also means less e-waste. Therefore, we surmise that GaN is potentially a more sustainable and more resilient component in power electronics supply chains.
Gallium is also important for future generations of power semiconductor materials. Ga2O3 has a band gap even larger than those of GaN and SiC (4.8 eV) and has a very high critical electric field strength, making it ideal for high voltage applications. It also has the advantage over other potential materials of being easier and cheaper to manufacture into devices. However, there are intrinsic issues with Ga2O3 such as its low thermal conductivity, much lower than that of silicon, and the difficulty of making a good p-type semiconductor. Currently, REWIRE at the University of Bristol with Cambridge and Warwick researchers are working on these challenges, and solutions are just around the corner.
But device breakthroughs and the advantages of gallium-containing semiconductors hinge critically on securing stable and reliable supplies of highly pure gallium. Currently, the compound semiconductor supply chain faces significant vulnerabilities, particularly due to recent geopolitical tensions – most notably, China’s imposition of export restrictions on critical minerals, which were introduced in response to the United States’ earlier trade tariffs under the Trump administration.
Caption: Semiconductor critical mineral risk matrix, per S&P Global’s analysis as of January 2025. Source – Are critical minerals trump card in US-China chip showdown?, S&P Global, 2025 (details of thresholds that were used and how they were determined are available in the source documentation).
China dominates the global production and purification of gallium, primarily because gallium is produced as a byproduct of aluminium and zinc refining—a process heavily concentrated within China. This historical dominance in extraction and purification capabilities has placed China in a strategic position, allowing it to influence global markets by adjusting export policies, thereby underscoring the inherent vulnerability and instability of relying heavily on a single geographical region. Furthermore, gallium’s status as a byproduct mineral exacerbates these supply chain risks. Unlike many strategic minerals, gallium cannot be easily stockpiled because its low melting point leads to a shelf life of less than a year. This inherently limits flexibility in responding to sudden geopolitical or economic shocks.
To mitigate these vulnerabilities, global supply chain resilience becomes paramount. Collaboration among governments, industry, and academia is essential. International partnerships and policies supporting local sourcing, recycling initiatives, and investments in technological innovation are crucial.
The University of Bristol Business School team in REWIRE is proactively addressing these issues. By adopting an interdisciplinary approach, REWIRE collaborates closely with industrial stakeholders and policymakers to develop tailored supply chain resilience toolkits specifically for the compound semiconductor industry.
References
- BGS (2024) – UK 2024 Criticality Assessment.
- U.S. Geological Survey (2022) – 2022 Final List of Critical Minerals.
- Deloitte (2023) – Critical minerals and the energy transition. Retrieved from https://www.deloitte.com/uk/en/issues/climate/critical-minerals.html
- U.S. Geological Survey (2022) – U.S. Geological Survey releases 2022 list of critical minerals.
- Time (2024) – Why Taiwan Is Becoming a Leader in Urban Mining.