ALUMINIUM NITRIDE AlN semiconductor: A long way to go

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In 2023, aluminum nitride was all over the internet, with netizens and tech enthusiasts calling it a “holy grail” of semiconductors. But where does it stand today? Is aluminum nitride a semiconductor only in papers? Find the truth about aluminum nitride and its status in 2025.

Aluminium Nitride is a 160-year-old compound commonly used as an electrical insulator in various applications. It exhibits an ultra-wide band gap (UWBG) to behave like an insulator, semiconductor, or superconductor under different experimental conditions.

AlN currently exists in two forms: hexagonal wurtzite and cubic zincblende. You can read about Aluminum Nitride and its properties in our 2023 article.

Why so much hype around the bandgap energy?

The semiconductor industry is betting on the potential of wide bandgap semiconductors (WBG) like SiC (Silicon Carbide) and GaN (Gallium Nitride) to minimize hyper-reliance on silicon. As mentioned above, aluminum nitride is an UWBG with a bandgap energy of 6 eV, much higher than GaN (3.4 eV) and SiC (3.2 eV).

Band gap energy is the amount of energy required to make an electron jump from a low-energy valence band to a higher-energy conduction band. Once an electron enters the conduction band, it can roam freely under the application of an electric field, contributing to current flow. Our article on intrinsic vs extrinsic semiconductors details these concepts.

In WBG or UWBG semiconductors, the valence and conduction bands are far from each other-- not far enough to make them insulators. Higher bandgap leads to higher breakdown voltages, lower leakage currents, enhanced high-temperature performance, and high-frequency operation. These semiconductors are suitable for their use in power electronics.

Isn’t the bandgap of AlN too high for a semiconductor?

Due to the large bandgap Of 6 eV, aluminum nitride must be chemically doped to behave like a semiconductor. The p-type doping process is challenging. The AlN crystal growth process is difficult due to the high melting temperature. However, various researches show that AlN has been transitioned into a semiconductor.

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Where does aluminum nitride stand now?

Due to the higher energy bandgap, aluminum nitride is commonly used as an insulator in various applications. Aluminum nitride exhibits exceptional thermal conductivity and capabilities to operate at deep UV frequencies.

Applications of AlN insulators include ceramic substrates in optoelectronics, optical storage media, steel manufacturing, microwave packaging, heat sinks in power electronics, surface acoustic wave devices, and military applications.

Advancements in aluminium nitride

Whenever somebody tries to buy aluminum nitride semiconductors online, various search results pop up. All these search results show an insulating aluminum nitride substrate rather than an AlN semiconductor.

At present, AlN is a hard ceramic material rather than a semiconductor crystal. Semiconducting aluminum nitride is still under research and testing— not fully commercialized yet. The following section details the developments in AlN semiconductors.

New millennium efforts

Research to transform insulating AlN to a semiconductor takes us back to the early 2000s. In 2002, a program launched in the USA developed an electrically insulating layer of AlN deposited on a Sapphire substrate. The substrate is now used for Si wafer handling and fabrication of high-power AlGaN HEMTs. China and Japan were also actively involved in the research, focusing on AlN crystal growth but no breakthroughs are seen.

All roads lead to insulation

Insulating AlN wafers offer exceptional thermal conductivity in high-power electronics manufacturing, ensuring proper thermal management. Another increasing use of aluminum nitride is SoI technology (Silicon on Insulator). Using AlN as an insulator for silicon improves device performance and deals with parasitic capacitance.

AlN Diode

At the beginning of 2024, Nagoya University researchers developed a diode from AlN alloy. The device exhibits low resistance and can withstand an electric field greater than that of SiC and GaN. The team of researchers didn’t rely on chemical doping- the tougher process and chose polarization doping methodology instead.

The resulting diode from AlN and GaN alloy was fully functional. However, challenges related to polarization doping still prevail. The polarization doping process, although introduced in the 2000s, is complex and needs further testing for scalability and integration into existing fabrication processes.

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AlN Crystal

In 2023, the Materials Department at Fraunhofer IISB succeeded in growing a 43-mm crystal of AlN. The crystal exhibited capabilities for further technological processing. The team processed a 1-inch wafer from the crystal structure. They further trimmed wafer slices as per semiconductor fabrication procedures.

The resulting material showcased stability at lower production costs. However, AIN’s hazardous environmental exposure was a subject of concern. If mass-produced, the thermal properties of AlN could surpass the shared monopoly of SiC and GaN in high-power electronics. So far, news about advancements in the commercial use of the crystal is still awaited.

AlN MOSFET

A paper published in the Journal of Physics demonstrates the fabrication of aluminum nitride MOSFET on a sapphire substrate. The researchers used a recessed gate structure and Ti-based contacts for improvement. Commonly used in WBG semiconductors, a recessed gate structure- the gate electrode is placed in a shallow trench-like structure (recess) and etched into the surface of the semiconductor.

The researchers studied Ti-based contacts through the annealing process at different temperatures. All the samples taken at different temperatures showcased a non-linear behavior, unable to produce an adequate amount of current. An optimal contact resistance improved switching speed and power loss but merely for 30 seconds. The AlN MOSFET still needs improvement to become a commercially viable option.

AlN x Ferroelectrics

Recently, researchers in China explored the possibilities of integrating aluminum nitride semiconductors and ferroelectric materials. Combining the benefits of ultra-wide bandgap semiconductors and ferroelectrics enables high-frequency operation, high-temperature performance, and low power consumption.

Ferroelectricity was analyzed for doped AlN. The researchers tested various methodologies for AlN crystal growth. The resulting material had high defects and exhibited high leakage current. The defects influenced ferroelectric properties, further challenging integration into fabrication units and market entry.

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100-mm crystal

Crystal IS, a New York-based high-performance LED manufacturer has announced commercially available 100-mm single-crystal aluminum nitride substrates. These substrates offer 99 % reusable area with high-performance integrating capabilities to existing GaN standards.

100-mm AlN substrates are applicable in power electronics and RF devices, reducing system size and improving efficiency. However, high production costs are limiting their scalability and industry adoption. In conclusion, research is still going on to improve the design, performance, and production capabilities of 100-mm AlN substrates.

Hopes for widespread commercialization?

The first-generation semiconductors were Si and Ge. The second-generation semiconductors were compound semiconductors like InP, GaAs, InGaAs, InGaAsP, and many more. Both direct band gap and indirect band gap semiconductors, including SiC and GaN, are third-generation semiconductors.

AlN is also a third-generation direct band gap semiconductor, following the path of SiC and GaN. Both SiC and GaN were studied and researched for long, before their eventual commercialization. Assuming a similar fate facilitated by the age of AI, AlN semiconductors are on the verge of commercialization— probably around the 2030s! However, as of 2025, AlN is an insulator in the market and a semiconductor on the internet.

References

• https://www.iisb.fraunhofer.de/en/press_media/press_releases/pressearchiv/archiv_2023/1-inch-AlN-wafer.html

• https://spectrum.ieee.org/aluminum-nitride

• https://www.power-and-beyond.com/aluminium-nitride-the-semiconductor-of-the-future-a-cbded96a594a13720644c5653a3050af/

• https://www.mdpi.com/2304-6740/13/2/29

• https://iopscience.iop.org/article/10.1088/1361-6463/ad8759

• https://spectrum.ieee.org/tag/iedm

• https://www.cisuvc.com/the-future-of-aluminum-nitride-ain-substrates-powering-tomorrows-technologies/

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