Aluminum nitride single-crystal growth


Aluminum nitride (AlN) exhibits remarkable and hugely interesting physico-chemical properties from a technological point of view such as combining high thermal conductivity with electrically insulating behavior when of high purity. It is also identified as a wide band-gap III-V semiconductor (6.2 eV). Table 1. Sums up some of the key physical properties of the AlN material.

Table 1. Key physical properties of AlN

Crystalline structure

Hexagonal Würtzite (2H)

Lattice parameter a and c

A=3.112 Å and c= 4.982

Melting point

> 2500 °C

Band gap

6.2 eV

Electrical resitivity

>1010 Ω cm

Thermal conductivity

330 W.m-1.K-1

Young modulus

308 GPa

Refractive index

2.1 – 2.2 (single crystalline)

AlN plays an increasingly important role in present and future technologies along with Gallium Nitride (GaN) and Silicon Carbide (SiC) in the telecommunication industry and high frequency/power electronics.

Growth techniques

One has to distinguish single and polycrystalline AlN. In its polycristalline form, AlN is mostly used as a protective coating and/or heat dissipation layer. Fabrication techniques such as sputtering and sintering are well developed and commercially available to fabricate such coatings.

In its single crystalline form, AlN is at the moment less prone to large scale industrialization owing to the difficulties (both technically and scientifically) in depositing highly crystalline insulating thin layers on foreign substrates.


And yet, the single crystalline AlN thin layer technology is a key aspect in developing applications such as filters/resonators/sensors (based on SAW/BAW devices) possibly operating in harsh environment and in the high frequency range (GHz and above). In these applications, the piezoelectric properties along the c-axis of the material is exploited. In the telecommunication industry, these devices are in huge demand, especially in an ever more connected environment (eg. 5G, IoT) and where reliability, miniaturization and high speed matters High power/frequency electronics is also an area where AlN and other wide band gap semiconductors find important use cases.

Our mission at Sil’Tronix ST

At Sil’Tronix ST, in close collaboration with the SIMaP laboatory (featuring a long experience in AlN thin film growth), we are working hard to control the growth process and make our growth technique (Hydride Vapour Phase Epitaxy or “HVPE”) fully scalable. 

AlN growth on sapphire

Large surface HVPE reactor for single crystalline (epitaxial) AlN growth on sapphire

We have developed a large surface automated high temperature chemical vapor deposition (HVPE) process which enables us to uniformly coat sapphire wafers up to 100 mm in diameter with high quality AlN layers up to 1 µm thick. This growth technique leads to superior physico-chemical properties such as high crystallinity (rocking curve <1000 arcsec AlN (002)) and low residual contamination levels (C, Si, O < 1017 at/cm3) making our layers effectively electrically insulating.

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