Authors:
Wang Guangzu, Zhengzhou Research Institute for Abrasives & Grinding
Diamond has been widely applied in various fields owing to its outstanding physical and chemical properties. As an indirect wide-bandgap semiconductor, diamond possesses a bandgap of approximately 5.2 eV, an extremely high thermal conductivity of up to 22 W/(cm·K), and room-temperature electron and hole mobilities of 4500 cm²/(V·s) and 3380 cm²/(V·s), respectively—values significantly higher than those of third-generation semiconductor materials such as GaN and SiC. Consequently, diamond demonstrates great potential for applications in high-temperature, high-power electronic devices as well as high-frequency, high-power microwave devices.
In addition, diamond exhibits an exciton binding energy as high as 80 meV, enabling strong free-exciton emission at room temperature, with an emission wavelength of approximately 235 nm. This makes diamond a promising candidate for the fabrication of high-power deep-ultraviolet light-emitting diodes (DUV LEDs). Diamond also plays an important role in the development of extreme ultraviolet (EUV), deep ultraviolet (DUV), and high-energy particle detectors.
Although significant challenges remain in the growth of diamond semiconductor materials and the fabrication of related devices, it is foreseeable that diamond-based semiconductor materials and devices may drive major technological breakthroughs in the near future. Therefore, diamond holds enormous potential in the field of power semiconductor device manufacturing.
At present, the application of diamond semiconductors in new materials, devices, and technologies is undergoing rapid development. Worldwide, intensive research efforts are being devoted to diamond semiconductors, and continuous innovation is expanding their application prospects across multiple industries. To accelerate breakthroughs in key technologies such as high-quality, large-area diamond wafers, researchers and industry experts from multiple disciplines are actively collaborating. It is widely believed that power diamond materials will eventually move beyond the laboratory and achieve commercial deployment.
After years of sustained research and development, diamond semiconductors are gradually moving toward practical applications. However, as a typical hard and brittle material, diamond remains extremely difficult to machine. Currently, common cutting methods include waterjet cutting, electrical discharge machining (EDM), and laser cutting.
Laser cutting is a precision machining technique capable of processing nearly all materials. Its principle involves focusing a high-power-density laser beam onto the workpiece, causing rapid melting, vaporization, ablation, or ignition of the irradiated material. Simultaneously, molten material is expelled by a high-speed coaxial gas jet, thereby achieving material separation.
Despite the strong appeal of diamond to the semiconductor industry, its application has been constrained by the lack of efficient slicing technologies. At present, diamond wafers must still be synthesized individually, resulting in high manufacturing costs and limiting large-scale industrial adoption.
According to information released by Chiba University (Japan), a research team led by Professor Hirofumi Hidai from the Graduate School has achieved a breakthrough in this area. The team developed a novel laser slicing technique that employs pulsed laser irradiation to slice diamond into thin plates, paving the way for next-generation semiconductor materials. This technique enables precise cutting along optimal crystallographic planes, producing diamond wafers with smooth surfaces.
The properties of crystalline materials, including diamond, vary with crystallographic orientation. A crystal plane is an imaginary plane that contains atoms within the crystal lattice. Although diamond can be relatively easily cleaved along certain planes, cutting often induces crack propagation along cleavage planes. For example, cutting along the {111} plane is relatively easy, whereas cutting along the {100} plane is far more challenging because cracks tend to propagate along the {111} cleavage planes, leading to material loss.
To suppress crack propagation, the researchers developed an innovative diamond processing technique. Instead of directly cutting the wafer grid, short-pulse laser beams are focused into a narrow conical region inside the material. Professor Hidai explained that the focused laser irradiation transforms diamond into amorphous carbon with a density lower than that of diamond. The resulting low-density grid lines act as predefined fracture paths within the diamond structure.
After this treatment, diamond wafers with regular geometries can be easily separated, providing well-prepared substrates for subsequent manufacturing processes. Overall, this technology represents a critical step toward establishing diamond as a next-generation semiconductor material. As Professor Hidai emphasized, the ability to fabricate high-quality diamond wafers at low cost is indispensable for diamond semiconductor device manufacturing, and this research brings that goal significantly closer.
As a semiconductor material, diamond features high optical phonon energy, the highest known electron and hole mobilities, and the highest thermal conductivity among all known semiconductors. These properties enable diamond to meet future demands for high power, strong electric fields, and radiation resistance, making it an ideal material for power semiconductor devices.
In recent years, diamond semiconductors have attracted widespread attention as candidates for next-generation high-frequency, high-power electronic devices. Although impressive device performance has been demonstrated, the operational lifetime of diamond-based power devices remains far below expectations due to current technical limitations, leaving substantial room for further improvement.
Diamond semiconductors possess a wide bandgap of 5.47 eV. In the field of deep-ultraviolet optoelectronics, diamond offers inherent advantages for detectors operating under extreme conditions, owing to its wide bandgap, high-temperature tolerance, and radiation resistance.
Diamond detectors are characterized by small size, strong radiation hardness, and fast response speed, making them particularly advantageous in nuclear radiation detection. However, the large-scale application of diamond detectors is still constrained by the availability of high-quality single-crystal diamond materials, as detection performance is highly sensitive to internal impurities and defects.
With the rapid advancement of electronic technology, semiconductor materials continue to evolve, while integrated circuits are progressing toward larger scale, higher integration density, and higher power output. Statistics indicate that more than 55% of electronic device failures are caused by excessive temperatures. If heat cannot be dissipated effectively, localized overheating may degrade performance or even lead to device burnout. Consequently, the development of advanced thermal management technologies has become an urgent requirement for ensuring device reliability and stability.
As the material with the highest thermal conductivity found in nature, diamond has attracted considerable attention as a substrate material capable of achieving near-perfect heat dissipation in high-power devices. Expanding the crystal size of CVD diamond substrates and achieving high-speed growth of single-crystal diamond are prerequisites for producing high-quality, large-area diamond semiconductor materials.
Currently, three main methods are used to prepare large-area single-crystal diamond via MPCVD: the repeated growth method, the three-dimensional growth method, and the mosaic (tiling) growth method.
Repeated growth method:
During growth, the sample is periodically removed for polishing and cleaning of the growth surface, after which growth resumes. This cycle is repeated multiple times to achieve larger diamond thickness. Surface polishing removes step bunching and polycrystalline regions, ensuring subsequent growth quality. While this method enables substantial vertical growth, it offers limited lateral expansion and is therefore ineffective for significantly enlarging crystal area.
Three-dimensional growth method:
This method combines repeated growth. Diamond is first grown to a certain thickness on the (100) surface, polished, and then growth proceeds on the (010) surface. This process is repeated to achieve large-area single crystals. However, frequent interruptions tend to degrade crystal quality, and repeated growth and surface treatment result in low efficiency and high cost.
Mosaic (tiling) growth method:
In this approach, multiple small square diamond substrates with identical size, thickness, and crystallographic orientation are tiled together, followed by epitaxial growth of a large-area single crystal. The key requirement is precise alignment of crystal orientations; even minor deviations can severely affect epitaxial quality. Compared with the other two methods, mosaic growth offers clear advantages in producing large-area single-crystal diamond with relatively high quality (except at the interfaces). However, perfect matching between individual substrates remains difficult, and defects or cracking may occur at the joints.
By contrast, the mosaic method provides a faster and more practical pathway to large-size single crystals (as shown in Figures 1 and 2). Hideaki Yamada et al. successfully synthesized multiple half-inch single-crystal diamond plates using ion implantation lift-off techniques, with crystal properties identical to those of the seed crystals. High-quality plates were selected and tiled into a mosaic substrate, followed by epitaxial growth and repeated lift-off and deposition processes, ultimately yielding large-area single-crystal diamond wafers.
Although current wafer sizes still fall short of the requirements for diamond semiconductor applications—generally considered to be at least two inches—the mosaic approach offers an effective solution for large-area single-crystal growth. With continued process optimization, surface quality issues arising from mosaic interfaces are expected to be gradually resolved.
Figure 1: Schematic of three-dimensional growth process
Figure 2: Schematic of mosaic growth process for large-area single-crystal diamond
At present, the high production cost of single-crystal diamond continues to limit its market adoption. Reducing production cost is essential for expanding the market value of diamond, and the only viable pathway is to improve efficiency through batch production. Since Asmussen et al. successfully demonstrated simultaneous growth of nearly 100 diamond seeds using 915 MHz MPCVD, large-scale multi-seed growth has become a major research focus. Multi-wafer growth is now regarded as a key direction for improving production efficiency.
With the rapid expansion of the semiconductor industry, demand for high-performance materials is increasing. Diamond semiconductor devices offer outstanding physical properties, including high thermal conductivity, high breakdown electric field strength, and high carrier mobility. These advantages significantly reduce energy loss, enable rapid heat dissipation, and extend device lifetime. Notably, diamond devices can sustain 50,000 times higher output power and 1,200 times higher operating frequency than silicon-based devices, highlighting their enormous potential in power semiconductor applications.
At present, diamond semiconductors are experiencing rapid development in new materials, devices, and technologies. Global research efforts continue to intensify, and ongoing innovation is opening broader application opportunities across industries. To advance breakthroughs in key technologies such as high-quality, large-area diamond wafers, interdisciplinary collaboration between researchers and industry experts is accelerating. It is expected that power diamond materials will soon transition from laboratory research to commercial applications.
Diamond semiconductors not only offer high computational speed but also exceptional high-temperature resistance. Silicon wafers typically tolerate temperatures below 300°C, gallium arsenide below 400°C, whereas diamond can withstand temperatures approaching 700°C without degradation. Moreover, diamond exhibits the highest thermal conductivity of all materials, with heat transfer rates approximately 30 times faster than silicon. As a result, high-power diamond semiconductor devices can operate without additional cooling systems, making diamond an ideal material for integrated circuits.
The large-scale development of diamond semiconductors may depend on silicon technology approaching its physical limits. Once silicon-based technologies encounter intrinsic bottlenecks, the superior performance of diamond semiconductors will gain widespread recognition and accelerate commercialization. At that stage, diamond may dominate the semiconductor market, ushering in a new “Diamond Era.”
Although diamond semiconductors still face numerous challenges, their long-term prospects remain highly promising. The evolution of semiconductor materials began with germanium, transitioned to silicon, and may next be led by silicon carbide. SiC shares a similar structure with diamond but contains silicon atoms, effectively representing “half a diamond.” It is likely to serve as a transitional material between the silicon era and the diamond semiconductor era.
Ultimately, diamond is expected to become the mainstream semiconductor material of the future. The historical trajectory of semiconductor materials follows Group IV of the periodic table—from germanium to silicon, to silicon carbide, and finally to carbon in the form of diamond. Beyond carbon, no higher element exists within this group. Once diamond becomes dominant, the semiconductor material system may reach long-term stability. If no material can ultimately replace diamond, the phrase “Diamond is Forever” may prove to be more than just a metaphor.