The application potential for diamond material is immense and it becomes an even more attractive material when it can be grown into large single crystals. Just as in silicon, single crystal material is ideal for integrated circuits and high power applications, but unlike silicon it is extremely difficult to get in high purity and high crystallinity to scale up to significant areas adopt processing technologies from the semiconductor industry. However, this has been the case for silicon in the early years (before fabs and processing equipment became standardized) and every other semiconductor material since (i.e., GaAs, InP, GaN, and SiC). For SiC, while 50mm wafers hit the market in 1999, it has taken the last 20+ years to achieve consistent 200mm wafers for use in fully depreciated [silicon] fabs. And this timeline was helped immensely by the SiC and GaN on SiC LED developments in the 1990s.1,2 So, the adoption of diamond into electronic devices is following a similar route of previous semiconductor materials, just in its own timescale as researchers overcome the hurdles associated with such a paradigm shift.
Like SiC in the 1990s, heterogeneous structures are being heavily explored, using SiC or GaN on diamond particularly in power electronics. The superior thermal properties and high breakdown voltage of diamond is being leveraged more so than the electrical properties of diamond devices (high power switching, high frequency use3,4), as n-type doping of diamond is still a challenge in the industry. The accelerator community5 provides many more niche applications far removed from the electronics market. In particle accelerators, diamond has become the go-to material for simple windows, reflectors, lenses, and are incorporated into more complex assemblies. In these applications, the thermal properties, crystallinity and purity are key attributes, as diamond is used as an optical material with exceptional thermal properties. Of course, these optical devices (usually plates) have to be securely mounted mechanically with good thermal contact to get heat out of the system. Therefore, larger blocks of single crystal material are required and rather clever mounting schemes developed to reduce stress while maintaining good thermal contact.
For diamond, the market has not reliably progressed beyond 10x10mm. Many technologies (and government-funded programs) exist to accelerate the manufacturing of larger substrates while maintaining high purity and crystallinity. Presently, two technologies are used for diamond fabrication, or lab-grown diamonds: high-pressure high-temperature (HPHT) and chemical vapor deposition (CVD) growth techniques. These technologies produce lab-made diamonds, inaccurately referred to as ‘synthetic’ as they are not mined from the earth but are created in industrial laboratories. Often these lab-grown diamond materials have much higher quality than naturally occurring diamond materials, and supported the gem industry for many, many years. Diamonds grown through either method are identical to natural diamonds both chemically, physically, and optically. Large single crystal diamond stones can be grown through CVD6 although the best quality diamond material is grown on substrates generated by HPHT growth. The conundrum is that although the crystallinity achieved in HPHT growth is superior, typical HPHT growth systems generate diamond stone dimensions that are usually below 1cm3. CVD can grow much larger sized material (many cm3) although its crystalline quality greatly depends on the seed crystal quality, so HPHT seed crystals are used for high-end applications.
- “The golden age of silicon carbide: 25 years of innovation.” (2020) Compound Semiconductor 26 (6) pp. 38-42.
- “Shifting to 200mm silicon carbide.” (2021) Compound Semiconductor 27 (7) pp.20-24.
- “Diamond Shines in High-Power Devices.” (2024) EE Times Europe, June 2024. https://www.eetimes.com/diamond-shines-in-high-power-devices/
- “High Voltage and High Power Diamond JFET Switch with Improvements,” Lawrence Livermore National Laboratory, https://ipo.llnl.gov/technologies/energy-and-environment/high-voltage-and-high-power-diamond-jfet-switch-improvements
- Stoupin, S., et al., “Large surface area diamond (111) crystal plates for applications in high heat load wavefront preserving X-ray crystal optics,” J. Synchrotron Rad. 23 1118–1123 (2016). J. Synchrotron Rad. (2016). 23, 1118–1123
- https://www.researchgate.net/publication/236544297_Prospects_for_Large_Single_Crystal_CVD_Diamonds