How Far Can a Diamond Be Stretched? Enough to Express Optoelectronic PropertiesJanuary 16, 2021 by Luke James
In semiconductor research, diamonds are much more than jewelry. A new study suggests that strain engineering may be the key to unlocking the optoelectronic merits of this material.
We all know that diamonds are among the toughest, most exceptional natural materials, equipped with a range of extreme physical properties that make them highly desirable. Its potential stretches far beyond its use in jewelry, however. It also holds great potential as an electronic material.
Stretching microfabricated diamonds could enable applications in next-gen microelectronics, researchers state. Image used courtesy of Dang Chaoqun / City University of Hong Kong
Recently, a joint research team at the City University of Hong Kong’s (CityU) joint research team used a nanomechanical approach to demonstrate the uniform elasticity of microfabricated diamond arrays. The researchers say their findings have shown the potential for strained diamonds as potential candidates for devices in next-generation microelectronics, quantum information technologies, and photonics.
Diamond as an Electronic Material
The theoretical potential of diamond in electronics applications isn’t exactly a new discovery. In fact, researchers have for some time now been sizing up diamond technology as a potential replacement for silicon when Moore’s Law comes to its inevitable end.
The potential of diamonds lies in their structure. Diamond is a wide-bandgap semiconductor. Its properties could, in theory, enable electronic devices that are beyond the scope of current systems when it comes to power handling capacity and operating voltage. For example, a diamond can conduct heat five times better than copper and 22 times better than silicon. It’s also both an excellent conductor and insulator, and its high dielectric strength means that thin diamond layers can isolate much larger voltages than current technologies.
A comparison of various semiconducting materials and their power handling vs. operating frequency. Image used courtesy of AKHAN Semiconductor
These metrics point to the potential for better electronics. But diamonds in their raw natural form can’t simply be used in electronic design. The material needs to be doped, and the diamond’s large bandgap and tight crystal structure make this difficult. This issue of doping has hamstrung the development of diamond technology and its use in electronics applications.
What is Strain Engineering?
Researchers have been experimenting with alternative solutions to doping, one of which is a method known as “strain engineering.” Strain engineering is when a large lattice strain is applied to the material to change its electronic band structure and functional properties.
Conducting strain engineering on diamonds was initially thought to be impossible for diamonds due to their strength. However, in 2018, the CityU research team led by Dr. Lu Yang, working with researchers from Harbin Institute of Technology (HIT) and Massachusetts Institute of Technology (MIT), found that nanoscale diamonds under unexpected large local strain can be elastically bent.
Based on this discovery, the team’s latest study demonstrated how this phenomenon could be used to develop functional diamond-based devices.
Researchers Create a "Diamond Bridge"
The first step in the team's process was to create microfabricated single-crystalline diamond samples from solid diamond single crystals in a bridge-like shape. These bridges were then stretched with an electron microscope.
Image of microfabricated diamond bridge samples under tensile strain. Image courtesy of Dang Chaoqun / City University of Hong Kong.
When the diamond bridges underwent cycles of continuous loading and unloading, they demonstrated large elastic deformation—one that was highly uniform—of roughly 7.5% strain. This upended the researchers' expectations of deformation in a localized area. By optimizing the sample geometry, they achieved a maximum tensile strain of up to 9.7%, which is close to the theoretical elastic limit of a diamond.
The team also performed density functional theory calculations, indicating that the diamond’s bandgap generally decreased as the tensile strain increased. These results demonstrated that the bandgap could change from indirect to direct, meaning that an electron could directly emit a photon and potentially enable efficient optoelectronic applications.
According to the researchers, these findings are an important early step in achieving deep elastic strain engineering of microfabricated diamonds. With further development and research, this process and the use of microfabricated diamonds could lead to different applications, from microelectronic systems to strain-engineered transistors.
Check Out More Diamond Semiconductor Research
Diamonds have long been a study of interest for wideband-gap semiconductors. Learn about more related research studies from the past few years.