Aluminium nitride

AlN was first synthesized in 1862 by F. Briegleb and A. Geuther.{{cite book|page=11 | author1= Fesenko I. P. | author2= Prokopiv M. M. | author3= Chasnyk V. I. |display-authors=etal | date = 2015| title = Aluminium nitride based functional materials, prepared from nano/micron-sized powders via hot pressing/pressureless sintering | publisher = EPC ALCON | isbn = 978-966-8449-53-6}}{{cite journal | last1=Briegleb | first1=F. | last2=Geuther | first2=A. | title=Ueber das Stickstoffmagnesium und die Affinitäten des Stickgases zu Metallen | journal=Justus Liebigs Annalen der Chemie | volume=123 | issue=2 | date=1862 | pages=228–241 | doi=10.1002/jlac.18621230212 | url=https://zenodo.org/record/2344471 }}

AlN, in the pure (undoped) state has an electrical conductivity of 10⁻¹¹–10⁻¹³ Ω⁻¹⋅cm⁻¹, rising to 10⁻⁵–10⁻⁶ Ω⁻¹⋅cm⁻¹ when doped. Electrical breakdown occurs at a field of 1.2–1.8{{e|5}} V/mm (dielectric strength).

The material exists primarily in the hexagonal wurtzite crystal structure, but also has a metastable cubic zincblende phase, which is synthesized primarily in the form of thin films. It is predicted that the cubic phase of AlN (zb-AlN) can exhibit superconductivity at high pressures.{{cite journal | last1=Dancy | first1=G. Selva | last2=Sheeba | first2=V. Benaline | last3=Louis | first3=C. Nirmala | last4=Amalraj | first4=A. | title=Superconductivity in Group III-V Semiconductor AlN Under High Pressure | journal=Orbital - the Electronic Journal of Chemistry | publisher=Instituto de Quimica - Univ. Federal do Mato Grosso do Sul | volume=7 | issue=3 | date=2015-09-30 | issn=1984-6428 | doi=10.17807/orbital.v7i3.628 | doi-access=free }} In AlN wurtzite crystal structure, Al and N alternate along the c-axis, and each bond is tetrahedrally coordinated with four atoms per unit cell.

One of the unique intrinsic properties of wurtzite AlN is its spontaneous polarization. The origin of spontaneous polarization is the strong ionic character of chemical bonds in wurtzite AlN due to the large difference in electronegativity between aluminium and nitrogen atoms. Furthermore, the non-centrosymmetric wurtzite crystal structure gives rise to a net polarization along the c-axis. Compared with other III-nitride materials, AlN has a larger spontaneous polarization due to the higher nonideality of its crystal structure (P_sp: AlN 0.081 C/m² > InN 0.032 C/m² > GaN 0.029 C/m²).{{Cite journal |last=Ambacher |first=O |date=1998-10-21 |title=Growth and applications of Group III-nitrides |url=https://iopscience.iop.org/article/10.1088/0022-3727/31/20/001 |journal=Journal of Physics D: Applied Physics |volume=31 |issue=20 |pages=2653–2710 |doi=10.1088/0022-3727/31/20/001 |s2cid=250782290 |issn=0022-3727}} Moreover, the piezoelectric nature of AlN gives rise to internal piezoelectric polarization charges under strain. These polarization effects can be utilized to induce a high density of free carriers at III-nitride semiconductor heterostructure interfaces completely dispensing with the need of intentional doping. Owing to the broken inversion symmetry along the polar direction, AlN thin film can be grown on either metal-polar or nitrogen-polar faces. Their bulk and surface properties depend significantly on this choice. The polarization effect is currently under investigation for both polarities.

Critical spontaneous and piezoelectric polarization constants for AlN are listed in the table below:{{Cite journal |last1=Ambacher |first1=O. |last2=Foutz |first2=B. |last3=Smart |first3=J. |last4=Shealy |first4=J. R. |last5=Weimann |first5=N. G. |last6=Chu |first6=K. |last7=Murphy |first7=M. |last8=Sierakowski |first8=A. J. |last9=Schaff |first9=W. J. |last10=Eastman |first10=L. F. |last11=Dimitrov |first11=R. |last12=Mitchell |first12=A. |last13=Stutzmann |first13=M. |date=2000-01-01 |title=Two dimensional electron gases induced by spontaneous and piezoelectric polarization in undoped and doped AlGaN/GaN heterostructures |journal=Journal of Applied Physics |volume=87 |issue=1 |pages=334–344 |doi=10.1063/1.371866 |issn=0021-8979|doi-access=free |bibcode=2000JAP....87..334A }}

AlN has high thermal conductivity, high-quality MOCVD-grown AlN single crystal has an intrinsic thermal conductivity of 321 W/(m·K), consistent with a first-principle calculation.{{cite journal | url = https://journals.aps.org/prmaterials/abstract/10.1103/PhysRevMaterials.4.044602 | title = Experimental observation of high intrinsic thermal conductivity of AlN | year = 2020 | doi = 10.1103/PhysRevMaterials.4.044602 | access-date = 2020-04-03 | last1 = Cheng | first1 = Zhe | last2 = Koh | first2 = Yee Rui | last3 = Mamun | first3 = Abdullah | last4 = Shi | first4 = Jingjing | last5 = Bai | first5 = Tingyu | last6 = Huynh | first6 = Kenny | last7 = Yates | first7 = Luke | last8 = Liu | first8 = Zeyu | last9 = Li | first9 = Ruiyang | last10 = Lee | first10 = Eungkyu | last11 = Liao | first11 = Michael E. | last12 = Wang | first12 = Yekan | last13 = Yu | first13 = Hsuan Ming | last14 = Kushimoto | first14 = Maki | last15 = Luo | first15 = Tengfei | last16 = Goorsky | first16 = Mark S. | last17 = Hopkins | first17 = Patrick E. | last18 = Amano | first18 = Hiroshi | last19 = Khan | first19 = Asif | last20 = Graham | first20 = Samuel | journal = Physical Review Materials | volume = 4 | issue = 4 | page = 044602 | arxiv = 1911.01595 | bibcode = 2020PhRvM...4d4602C | s2cid = 207780348 }} For an electrically insulating ceramic, it is 70–210 W/(m·K) for polycrystalline material, and as high as 285 W/(m·K) for single crystals).{{cite web | url = http://www.ioffe.rssi.ru/SVA/NSM/Semicond/AlN/index.html | work = Ioffe Database | title = AlN – Aluminium Nitride | publisher = FTI im. A. F. Ioffe, RAN | location = Sankt-Peterburg | access-date = 2014-01-01 }}

AlN is one of the few materials that have both a wide and direct bandgap (almost twice that of SiC and GaN) and large thermal conductivity.{{Cite journal |last1=Hickman |first1=Austin Lee |last2=Chaudhuri |first2=Reet |last3=Bader |first3=Samuel James |last4=Nomoto |first4=Kazuki |last5=Li |first5=Lei |last6=Hwang |first6=James C M |last7=Grace Xing |first7=Huili |last8=Jena |first8=Debdeep |date=2021-04-01 |title=Next generation electronics on the ultrawide-bandgap aluminum nitride platform |journal=Semiconductor Science and Technology |volume=36 |issue=4 |pages=044001 |doi=10.1088/1361-6641/abe5fd |s2cid=233936255 |issn=0268-1242|doi-access=free |bibcode=2021SeScT..36d4001H }} This is due to its small atomic mass, strong interatomic bonds, and simple crystal structure.{{Cite journal |last1=Xu |first1=Runjie Lily |last2=Muñoz Rojo |first2=Miguel |last3=Islam |first3=S. M. |last4=Sood |first4=Aditya |last5=Vareskic |first5=Bozo |last6=Katre |first6=Ankita |last7=Mingo |first7=Natalio |last8=Goodson |first8=Kenneth E. |author-link8=Kenneth E. Goodson |last9=Xing |first9=Huili Grace |last10=Jena |first10=Debdeep |last11=Pop |first11=Eric |author-link11=Eric Pop |date=2019-11-14 |title=Thermal conductivity of crystalline AlN and the influence of atomic-scale defects |url=https://aip.scitation.org/doi/10.1063/1.5097172 |journal=Journal of Applied Physics |volume=126 |issue=18 |pages=185105 |arxiv=1904.00345 |bibcode=2019JAP...126r5105X |doi=10.1063/1.5097172 |issn=0021-8979 |s2cid=90262793}} This property makes AlN attractive for application in high speed and high power communication networks. Many devices handle and manipulate large amounts of energy in small volumes and at high speeds, so due to the electrically insulating nature and high thermal conductivity of AlN, it becomes a potential material for high-power power electronics. Among group III-nitride materials, AlN has higher thermal conductivity compared to gallium nitride (GaN). Therefore, AlN is more advantageous than GaN in terms of heat dissipation in many power and radio frequency electronic devices.

Thermal expansivity is another critical property for high temperature applications. The calculated thermal expansion coefficients of AlN at 300 K are 4.2×10⁻⁶ K⁻¹along a-axis and 5.3×10⁻⁶ K⁻¹ along c-axis.{{Cite journal |last1=Slack |first1=Glen A. |last2=Bartram |first2=S. F. |date=1975-01-01 |title=Thermal expansion of some diamondlike crystals |journal=Journal of Applied Physics |volume=46 |issue=1 |pages=89–98 |doi=10.1063/1.321373 |issn=0021-8979|doi-access=free |bibcode=1975JAP....46...89S }}

Aluminium nitride is stable at high temperatures in inert atmospheres and melts at about {{cvt|2200|C|K F}}. In a vacuum, AlN decomposes at ~{{cvt|1800|C|K F|abbr=on}}. In the air, surface oxidation occurs above {{cvt|700|C|K F|abbr=on}}, and even at room temperature, surface oxide layers of 5–10 nm thickness have been detected. This oxide layer protects the material up to {{cvt|1370|C|K F|abbr=on}}. Above this temperature bulk oxidation occurs. Aluminium nitride is stable in hydrogen and carbon-dioxide atmospheres up to {{cvt|980|C|K F|abbr=on}}.{{cite book | author = Berger, L. I. | title = Semiconductor Materials | publisher = CRC Press | year = 1997 | isbn = 978-0-8493-8912-2 | pages = [https://archive.org/details/semiconductormat0000berg/page/123 123]–124 | url = https://archive.org/details/semiconductormat0000berg | url-access = registration }}

The material dissolves slowly in mineral acids through grain-boundary attack and in strong alkalies through attack on the aluminium-nitride grains. The material hydrolyzes slowly in water. Aluminium nitride is resistant to attack from most molten salts, including chlorides and cryolite.{{Cite journal |last1=Pradhan |first1=S |last2=Jena |first2=S K |last3=Patnaik |first3=S C |last4=Swain |first4=P K |last5=Majhi |first5=J |date=2015-02-19 |title=Wear characteristics of Al-AlN composites produced in-situ by nitrogenation |journal=IOP Conference Series: Materials Science and Engineering |volume=75 |issue=1 |pages=012034 |doi=10.1088/1757-899X/75/1/012034 |s2cid=137160554 |issn=1757-899X |doi-access=free |bibcode=2015MS&E...75a2034P }}

Aluminium nitride can be patterned with a Cl₂-based reactive ion etch.{{cite journal |last1=Chih-ming Lin |last2=Ting-ta Yen |last3=Yun-ju Lai |last4=Felmetsger |first4=V. V. |last5=Hopcroft |first5=M. A. |last6=Kuypers |first6=J. H. |last7=Pisano |first7=A. P. |title=Temperature-compensated aluminum nitride lamb wave resonators |journal=IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control |date=March 2010 |volume=57 |issue=3 |pages=524–532 |doi=10.1109/TUFFC.2010.1443 |pmid=20211766 |s2cid=20028149}}{{cite journal |last1=Xiong |first1=Chi |last2=Pernice |first2=Wolfram H. P. |last3=Sun |first3=Xiankai |last4=Schuck |first4=Carsten |last5=Fong |first5=King Y. |last6=Tang |first6=Hong X. |title=Aluminum nitride as a new material for chip-scale optomechanics and nonlinear optics |journal=New Journal of Physics |date=2012 |volume=14 |issue=9 |pages=095014 |doi=10.1088/1367-2630/14/9/095014 |language=en |issn=1367-2630 |bibcode=2012NJPh...14i5014X |arxiv=1210.0975 |s2cid=118571039}}

AlN is synthesized by the carbothermal reduction of aluminium oxide in the presence of gaseous nitrogen or ammonia or by direct nitridation of aluminium.{{Cite journal |last1=Yamakawa |first1=Tomohiro |last2=Tatami |first2=Junichi |last3=Wakihara |first3=Toru |last4=Komeya |first4=Katsutoshi |last5=Meguro |first5=Takeshi |last6=MacKenzie |first6=Kenneth J. D. |last7=Takagi |first7=Shinichi |last8=Yokouchi |first8=Masahiro |date=2005-10-04 |title=Synthesis of AlN Nanopowder from γ-Al2O3 by Reduction-Nitridation in a Mixture of NH3-C3H8 |url=https://onlinelibrary.wiley.com/doi/10.1111/j.1551-2916.2005.00693.x |journal=Journal of the American Ceramic Society |language=en |volume=89 |issue=1 |pages=171–175 |doi=10.1111/j.1551-2916.2005.00693.x |issn=0002-7820 |access-date=2023-06-26}} The use of sintering aids, such as Y₂O₃ or CaO, and hot pressing is required to produce a dense technical-grade material.{{cn|date=October 2023}}

Epitaxially grown thin film crystalline aluminium nitride is used for surface acoustic wave sensors (SAWs) deposited on silicon wafers because of AlN's piezoelectric properties. Recent advancements in material science have permitted the deposition of piezoelectric AlN films on polymeric substrates, thus enabling the development of flexible SAW devices.{{Cite journal |last=Lamanna |first=Leonardo |date=November 2023 |title=Recent Progress in Polymeric Flexible Surface Acoustic Wave Devices: Materials, Processing, and Applications |journal=Advanced Materials Technologies |language=en |volume=8 |issue=21 |doi=10.1002/admt.202300362 |issn=2365-709X|doi-access=free }} One application is an RF filter, widely used in mobile phones,{{cite news |newspaper=Investor's Business Daily |author=Tsuruoka, Doug |date=2014-03-17 |url=http://news.investors.com/technology/031714-693520-aapl-drives-avgo-fbar-filter-shipments.htm?ven=rss |title=Apple, Samsung Cellphone Filter Orders Lift Avago}} which is called a thin-film bulk acoustic resonator (FBAR). This is a MEMS device that uses aluminium nitride sandwiched between two metal layers.{{cite web | url=http://www.en-genius.net/site/zones/wirelessZONE/product_reviews/hfp_052702 | title = ACPF-7001: Agilent Technologies Announces FBAR Filter for U.S. PCS Band Mobile Phones and Data Cards | work = wirelessZONE | publisher = EN-Genius Network Ltd. | date = 2002-05-27 | access-date = 2008-10-18 }}

AlN is also used to build piezoelectric micromachined ultrasonic transducers, which emit and receive ultrasound and which can be used for in-air rangefinding over distances of up to a meter.{{cite news | url=http://www.technologyreview.com/news/520841/a-gestural-interface-for-smart-watches/ | title = A Gestural Interface for Smart Watches |website=MIT Technology Review |last=Metz |first=Rachel | date = November 2013 |archive-url=http://web.archive.org/web/20131102010259/https://www.technologyreview.com/news/520841/a-gestural-interface-for-smart-watches/ |archive-date=Nov 2, 2013}}

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Metallization methods are available to allow AlN to be used in electronics applications similar to those of alumina and beryllium oxide. AlN nanotubes as inorganic quasi-one-dimensional nanotubes, which are isoelectronic with carbon nanotubes, have been suggested as chemical sensors for toxic gases.{{cite journal | last1 = Ahmadi | first1 = A. | last2 = Hadipour | first2 = N. L. | last3 = Kamfiroozi | first3 = M. | last4 = Bagheri | first4 = Z. | year = 2012 | title = Theoretical study of aluminium nitride nanotubes for chemical sensing of formaldehyde | journal = Sensors and Actuators B: Chemical | volume = 161 | issue = 1 | pages = 1025–1029 | doi = 10.1016/j.snb.2011.12.001 | bibcode = 2012SeAcB.161.1025A }}{{cite journal | last1 = Ahmadi Peyghan | first1 = A. | last2 = Omidvar | first2 = A. | last3 = Hadipour | first3 = N. L. | last4 = Bagheri | first4 = Z. | last5 = Kamfiroozi | first5 = M. | year = 2012 | title = Can aluminum nitride nanotubes detect the toxic NH₃ molecules? | journal = Physica E | volume = 44 | issue = 7–8 | pages = 1357–1360 | doi=10.1016/j.physe.2012.02.018 | bibcode = 2012PhyE...44.1357A }}

Currently there is much research into developing light-emitting diodes to operate in the ultraviolet using gallium nitride based semiconductors and, using the alloy aluminium gallium nitride, wavelengths as short as 250 nm have been achieved. In 2006, an inefficient AlN LED emission at 210 nm was reported.{{cite journal | author = Taniyasu, Y. | title = An Aluminium Nitride Light-Emitting Diode with a Wavelength of 210 Nanometres | journal = Nature | volume = 441 | year = 2006 | url = http://physicsworld.com/cws/article/news/2006/may/17/leds-move-into-the-ultraviolet | doi = 10.1038/nature04760 | pmid = 16710416 | issue = 7091 | pages = 325–328 |display-authors=etal | bibcode = 2006Natur.441..325T | s2cid = 4373542 }}

AlN-based high electron mobility transistors (HEMTs) have attracted a high level of attention due to AlN’s superior properties, such as better thermal management, reduced buffer leakage, and excellent integration for all nitride electronics. AlN buffer layer is a critical building block for AlN-based HEMTs, and it has been grown by using MOCVD or MBE on different substrates. Building on top of AlN buffer, n-channel devices with 2D electron gas (2DEG) and p-channel devices with 2D hole gas (2DHG) have been demonstrated. The combination of high-density 2DEG and 2DHG on the same semiconductor platform makes it a potential candidate for CMOS devices.

Aluminum oxide ceramics facilitate polymerization reactions, enhancing efficiency and consistency in creating plastics and resins.{{cite web |url=https://www.preciseceramic.com/blog/what-is-aluminum-nitride-ceramic.html |title=What is Aluminum Nitride Ceramic? |last=Ross |first=Lisa |date=Apr 12, 2024 |website=Advanced Ceramic Materials |access-date=Nov 2, 2024}} They are also used in microwave applications as a substrate and heat sink.{{cite journal |last1=Ma |first1=Yupu |last2=Wei |first2=Tao |year=2023 |title= Embedded Microfluidic Cooling in Aluminum Nitride HTCC Substrate for High-Power Radio Frequency Chip Array |journal= Journal of Thermal Science and Engineering Applications|volume=15 |issue=10 |pages=101004–101012 |doi=10.1115/1.4062400}} More researchers are examining the production of light-emitting diodes(LEDs) to operate in the ultraviolet region using aluminium gallium nitride(AlGaN) based semiconductors.{{cite journal |last1=Lang |first1=Jing |last2=Xu |first2=Fujun |year=2024 |title= Progress in Performance of AlGaN-Based Ultraviolet Light Emitting Diodes |journal=Advanced Electronic Materials |volume=11 |page=2300840 |doi=10.1002/aelm.202300840 |doi-access=free}}

Among the applications of AlN are

• opto-electronics,
• dielectric layers in optical storage media,
• electronic substrates, chip carriers where high thermal conductivity is essential,
• military applications,
• as a crucible to grow crystals of gallium arsenide,
• steel and semiconductor manufacturing.

• Boron nitride
• Aluminium phosphide
• Aluminium arsenide
• Aluminium antimonide
• Gallium nitride
• Indium nitride
• Aluminium oxynitride
• Titanium aluminium nitride, TiAlN or AlTiN

{{Reflist}}

• {{cite book|page=4.45 | editor= Haynes, William M. | date = 2016| title = CRC Handbook of Chemistry and Physics | edition = 97th | publisher = CRC Press | isbn = 9781498754293| title-link= CRC Handbook of Chemistry and Physics }}

{{Aluminium compounds}}

{{Nitrides}}

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Category:Nitrides

Category:Aluminium compounds

Category:Piezoelectric materials

Category:III-V semiconductors

Category:Light-emitting diode materials

Category:III-V compounds

Category:Wurtzite structure type