SEMICONDUCTOR MATERIALS Aluminium Nitride: The semiconductor of the future?

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Post the 160-year-old discovery, Aluminium Nitride has been one of the favorite compounds for researchers to study. Denoted by AlN, the compound has been recently launched as a semiconductor wafer by Fraunhofer IISB. This article details AlN structures, electrical properties, and its scope as a semiconductor.

Aluminium Nitride: An overview

Aluminium Nitride is a compound denoted by the chemical formula AlN. Aluminium (Z=13) carries an electric charge of “+3” to form covalent bonds with nitride- an electropositive compound of nitrogen (Z=7) carrying an electric charge of “-3”. The unique chemical characteristics of Aluminium Nitride enable it to behave like an insulator, semiconductor, and superconductor under different conditions. Aluminium Nitride exists in two forms: Hexagonal Wurtzite and Cubic Zincblende.

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Hexagonal Wurtzite

Under room temperature, the solid hexagonal wurtzite structure of Aluminium Nitride behaves like an insulator with a wide band gap of 6 eV. Upon doping the intrinsic structure, the electrical conductivity increases to support the semiconductor properties of the compound.

Cubic Zincblende

The cubic zincblende phase of Aluminium Nitride is a metastable structure that is said to form ionic bonds to replace the covalent character. According to the researchers, the compound might exhibit superconductivity under high-pressure environments.

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Better than SiC and GaN: Aluminium Nitride as a semiconductor

AlN is a potential semiconductor that could shape the industry and perform equivalent to SiC and GaN devices.

Properties of Aluminium Nitride

• Tolerant to radiation

• High thermal conductivity

• High volume resistivity

• High dielectric strength.

• High abrasion resistance.

• Low risk of fabrication contamination

• High breakdown field strength

• Low defects

• Strong mechanical capabilities

• Ability to behave like an insulator, semiconductor, and superconductor under different conditions

• Existence in two forms- hexagonal wurtzite and cubic zincblende structures

• Photoluminescence and piezoelectricity

• Suitable for plasma treatment

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However, some properties make AlN possibly a better choice than SiC and GaN.

Compared to SiC, AlN has high thermal conductivity and band gap energy that provides great electrical isolation and heat dissipation. GaN is stable enough to avoid thermal breakdown up to 2200-3000 °C. But SiC and GaN are less thermally stable for high-power electronics and RF applications that generate much heat. However, SiC has higher breakdown voltage and electron mobility to serve high-voltage applications.

A process known as epitaxy enables AlN wafer manufacturing. Recently, Fraunhofer IISB has manufactured a 1-inch AlN wafer from the crystal structure. The challenging process is increasing the crystal's lifetime, and availability and enhancing the stability at lower production costs. Another possible drawback is that AlN may become hazardous upon exposure to sunlight. However, it is used extensively in solar cells, power amplifiers, and RF filters.

Why could Aluminium Nitride revolutionize the power electronics industry?

Aluminium Nitride is used in various applications that require high thermal conductivity, capacity to withstand extreme radiation, and exceptional mechanical properties. These applications include laser diodes, UV LEDs, and space-related equipment. On a wider scale, AlN serves a variety of applications in the thin film microelectronics and power electronics industries.

In the power electronics and radio frequency industry, devices are required to operate at high frequencies and efficiently dissipate power. The electrical insulation property of AlN enables it to isolate itself from the application electrically. Such electrical isolation protects the device and allows high-power operation. AlN possesses excellent thermal conductivity that allows it to dissipate power efficiently and exhibit super-low power loss. The exceptional electrical, mechanical, and chemical properties may enable AlN to become one of the best UWBG semiconductors in the power electronics industry.

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