Sapphire is a widely used material for optical, electronic and semiconductor applications due to
its excellent optical properties and very high durability. Optical and mechanical properties of
sapphire depend on many factors such as the starting materials that are used to grow crystals,
methods to grow sapphire crystals, etc. Demand for highest purity and quality of sapphire crystals
increased ten fold for the last several years due to new applications for this material.
In this work we studied the effect of starting materials and crystal growth methods on the optical
and mechanical properties of sapphire, especially concentrating on the effect of hydrogen on the
properties of sapphire.
It was found that the infrared (IR) absorption which is traditionally used to measure the hydrogen
content in sapphire crystals cannot be reliably used and the data obtained by this method
provides a much lower hydrogen concentration than actual. We have shown for the first time that
Nuclear Magnetic Resonance techniques can be successfully used to determine hydrogen
concentration in sapphire crystals.
We have shown that hydrogen concentration in sapphire can reach thousands of ppm if these
crystals are grown from Verneuil starting material or aluminum oxide powder. Alternatively, the
hydrogen concentration is very low if sapphire crystals are grown from High Purity Densified
Alumina (HPDA®) as a starting material. HPDA® is produced by EMT, Inc through their
proprietary patented technology.
It was found that optical and mechanical properties of sapphire crystals grown using EMT HPDA®
starting material are much better than those sapphire crystals grown using a starting material of
Verneuil crystals or aluminum oxide powder.
Sapphire (single crystal aluminum oxide) is a material commonly used in optical, electronic and chemical applications due to its material properties.
Sapphire is usually used for optical applications due to its ability to transmit from the Ultra Violet (UV) wavelengths into the mid Infra-red (IR) wavelengths. The transmission characteristics of the material is determined by various factors, however the impurities content seems to play a significant role. These impurities can either come from the growth process or from the starting raw material (commonly called crackle).
We studied the effect of impurities of the starting raw material with specific interest in hydrogen's effect on the optical properties (absorption, transmission) of sapphire crystals grown by different growth techniques.
We have characterized these growth techniques into two categories:
A)Large Thermal Gradient Method: (Czochralski (Cz), Edge Defined Film Fed Growth (EFG) or Stepanov)
B.) Low Thermal Gradient Methods (Kyropoulos, Heat Exchange Method (HEM))
We used the following starting raw materials ("crackle"):
a. Vernuil crystals produced by different manufacturers
b. High purity aluminum oxide powder
c. High Purity Densified Alumina (EMT HPDAR) produced by EMT, Inc thru their proprietary patented technology.
Through Nuclear Magnetic Resonance (NMR) analytical techniques, it was found that the hydrogen concentration is very high in Vernuil crystals or in aluminum oxide powder. Consequently, sapphire crystals grown using Vernuil starting material or aluminum oxide powder also have a very high Hydrogen content.
Utilizing the same NMR analytical techniques, EMT HPDAR starting material showed very low Hydrogen concentration. Thus, sapphire crystals grown from EMT HPDAR starting material has a very low Hydrogen content.
It was found that optical properties in sapphire crystals grown using EMT HPDAR starting material are more uniform and have higher transmission than in sapphire crystals grown using as starting material aluminum oxide powder or Vernuil crystals.