Germanium Ge (N-type) Evaporation Process Notes
Germanium is a hard and brittle material with a semi-metallic, grayish-white appearance. It has a density of 5.35 g/cc, a melting point of 937°C, and a vapor pressure of 10-4 Torr at 1,167°C. It is classified on the periodic table as a metalloid, which means it possesses properties of metals and non-metals. Like silicon, germanium is a semiconductor and frequently utilized in the fabrication of transistors and integrated circuits. It is often evaporated under vacuum to create layers in the production of optical storage media and optical coatings. Other uses of the material are as an alloying agent and catalyst.
Germanium Ge (N-type) Specifications
|Color/Appearance||Grayish White, Semi-Metallic|
|Thermal Conductivity||60 W/m.K|
|Melting Point (°C)||937|
|Bulk Resistivity||5-40 ohm-cm|
|Coefficient of Thermal Expansion||6 x 10-6/K|
|Theoretical Density (g/cc)||5.32|
|Max Power Density|
|Type of Bond||Indium, Elastomer|
|Thermal Evaporation Techniques||
Boat: W, C, Ta
Crucible: Q, Al2O3
|E-Beam Crucible Liner Material||FABMATE®, Graphite|
|Temp. (°C) for Given Vap. Press. (Torr)||
|Comments||Excellent films from E-beam.|
* This is a recommendation based on our experience running these materials in KJLC guns. The ratings are based on unbonded targets and are material specific. Bonded targets should be run at lower powers to prevent bonding failures. Bonded targets should be run at 20 Watts/Square Inch or lower, depending on the material.
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.