Zinc Selenide (ZnSe) Pieces Evaporation Materials

Zinc Selenide (ZnSe) Pieces Overview

We sell these pellets and pieces by unit weight for evaporation use in deposition processes. These approximate materials prices are published to provide budgetary guidelines. Actual prices can vary and may be higher or lower, as determined by availability and market fluctuations. To speak to someone directly about current pricing, please click here .

Zinc Selenide (ZnSe) General Information

Zinc selenide is a chemical compound with a chemical formula of ZnSe. It is yellow to red in appearance with a melting point of >1,100°C, a density of 5.42 g/cc, and a vapor pressure of 10^-4 Torr at 660°C. Zinc selenide is heavily used as an infrared optical material. It is evaporated under vacuum for infrared optical coatings, more specifically, night vision optical coatings.

Zinc Selenide (ZnSe) Specifications

**** Suggestion based on previous experience but could vary by process. Contact local KJLC Sales Manager for further information

Z-Factors

Empirical Determination of Z-Factor

Unfortunately, Z Factor and Shear Modulus are not readily available for many materials. In this case, the Z-Factor can also be determined empirically using the following method:

• Deposit material until Crystal Life is near 50%, or near the end of life, whichever is sooner.
• Place a new substrate adjacent to the used quartz sensor.
• Set QCM Density to the calibrated value; Tooling to 100%
• Zero thickness
• Deposit approximately 1000 to 5000 A of material on the substrate.
• Use a profilometer or interferometer to measure the actual substrate film thickness.
• Adjust the Z Factor of the instrument until the correct thickness reading is shown.

Another alternative is to change crystals frequently and ignore the error. The graph below shows the % Error in Rate/Thickness from using the wrong Z Factor. For a crystal with 90% life, the error is negligible for even large errors in the programmed versus actual Z Factor.

Thermal Evaporation of Zinc Selenide (ZnSe)

We recommend thermally evaporating zinc selenide from a tantalum boat such as our EVS8B005TA. A tantalum baffle box, such as our EVSSO22, may also be used. Thermal evaporation is more commonly used for depositing optical films because stoichiometric films are easier to obtain with this method.

With an evaporation temperature of ~900°C and a base pressure of 10^-6 Torr, we anticipate a deposition rate of 10-15 angstroms per second. Pressure should be monitored to ensure outgassing is at an acceptable level before increasing power.

Due to its high vapor pressure at low temperatures, zinc selenide is typically evaporated in a dedicated vacuum chamber.

E-beam Evaporation of Zinc Selenide (ZnSe)

Zinc selenide can be e-beam evaporated with a tantalum or molybdenum crucible liner. However, thermal evaporation is more commonly used for depositing optical films because stoichiometric films are easier to obtain with this method.

We recommend to sweep the e-beam at low power to uniformly melt the material and avoid hole drilling. Evaporating at a low e-beam power will also help to avoid material dissociation. Pressure should be monitored to ensure outgassing is at an acceptable level before increasing the power. With an evaporation temperature of ~900°C, we anticipate a deposition rate of 10-15 angstroms per second. Substrate surface cleaning is required for good adhesion. Yttrium oxide (Y₂O₃), hafnium oxide (HfO₂), or fluorides can be used as a thin adhesion layer if necessary.

Another key process note is to consider the fill volume in the e-beam application because we find that the melt level of a material in the crucible directly affects the success of the crucible liner. Overfilling the crucible will cause the material to spill over and create an electrical short between the liner and the hearth. The outcome is cracking in the crucible. This is the most common cause of crucible liner failure. Placing too little material in the crucible or evaporating too much material before refilling can be detrimental to the process as well. When the melt level is below 30%, the e-beam is likely to strike the bottom or walls of the crucible which immediately results in breakage. Our recommendation is to fill the crucible between 2/3 and 3/4 full to prevent these difficulties.

Crucible liners should be stored in a cool, dry place and always handled with gloves or forceps.

Due to its high vapor pressure at low temperatures, zinc selenide is typically evaporated in a dedicated vacuum chamber.