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

Material Type	Germanium
Symbol	Ge (N-type)
Atomic Weight	72.63
Atomic Number	32
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
Sputter	DC
Max Power Density (Watts/Square Inch)	20*

Type of Bond	Indium, Elastomer
Dopant	Antimony
Z Ratio	0.516
E-Beam	Excellent
Thermal Evaporation Techniques	Boat: W, C, Ta Crucible: Q, Al₂O₃
E-Beam Crucible Liner Material	FABMATE^®, Graphite
Temp. (°C) for Given Vap. Press. (Torr)	10^-8: 812 10^-6: 957 10^-4: 1,167
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.

Thermal Evaporation of Germanium (Ge (N-type))

In a deposition system with normal dimensions, a material with an equilibrium vapor pressure (EVP) of 1E-2 Torr will deposit at a rapid rate. Therefore, 1E-2 Torr is typically regarded as the EVP one should attempt to achieve during deposition. The only parameter that affects EVP is temperature. We reference various charts or books to determine what temperature is needed to make the material's EVP 1E-2 Torr. Comparing that temperature with the material's melting point indicates whether the material will evaporate or sublime at that vapor pressure.

Germanium (Ge (N-type)) Vapor Pressure Chart

Germanium's melting point (937°C) is well below the temperature to reach 1E-2 Torr. Hence, germanium evaporates as opposed to subliming. We recommend that the base pressure for germanium evaporation should be 10^-6 Torr or lower with an evaporation temperature of 1,400°C. The average deposition rate under these parameters is 1-5 angstroms/sec.

Germanium can be thermally evaporated using a tantalum or tungsten dimple-style boat such as our EVS8B005W or EVS8B005TA. It is not known to alloy with refractory metals.

E-beam Evaporation of Germanium (Ge (N-type))

We recommend using either a graphite^® or FABMATE^® crucible liner for e-beam evaporating germanium. Sweeping the e-beam and incrementally ramping power to fully melt the evaporation pieces can help improve the deposition rate. Once melted, a focused beam can be used to deposit films.

Crucible liners will need to be replaced fairly often because liquid germanium has the tendency to damage liners. When germanium melts, it will mechanically bond to the inner walls of the crucible liner. Upon cooling or re-heating, the difference in thermal expansion/contraction of the germanium in contact with the liner can produce enough stress to break the liner. We also 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 maintain a melt level between 30-80% and slowly ramp power up and down to prevent these complications. However, even when following these guidelines, the liners will still need to be replaced frequently

We recommend that the base pressure for germanium evaporation should be 10^-6 Torr or lower with an evaporation temperature of 1,400°C. The average deposition rate under these parameters is 1-5 angstroms/sec. Germanium can also be evaporated directly from the copper hearth of the e-gun. Because not using a crucible liner is not always an option, especially in shared systems, some customers will use a copper crucible liner and place the pieces in the liner as opposed to placing directly in the hearth.

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

E-beam Crucible Liner Fill Rate Calculator

Instructions for use:
Input the Crucible Liner Volume, Select Material (if not available in menu, manually input Material Density in g/cm³), and input fill rate %.

KJLC recommends a fill rate between 67-75%. Overfilling the crucible will cause the material to spill over and create an electrical short between the liner and the hearth causing the crucible to crack. Placing too little material in the crucible or allowing the melt level to get too low 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.

The fill rate above assumes that the material is fully melted and does not take into account packing density. It should be noted that the crucible liner may need to be loaded multiple times, pre-melted, and topped off in order to achieve the final desired melt level/fill rate. When loading the crucible, do not load more than 80% of the height of the crucible liner.

This calculator is for estimation purposes only.

Crucible Liner Volume (in cc):

Material:

- or -
Density of the material in g/cm³:

Fill Rate %:

Result

See highlighted results that match your result in the table below.

Material Needed to Deposit a 1 Micron Film Calculator

Instructions for use:
Select source type, input distance from source to substrate and Select Material (if not available in menu, manually input Material Density in kg/m³).

This calculator is for estimation purposes only. The estimated mass is that needed to produce a desired film thickness (1 micron in this case) on a flat substrate at a point directly above the source, accounting for the approximate plume distribution of the selected source type. It does not account for any expected nonuniformity in thickness over a larger substrate area. More complex geometries, e.g. those with offset and/or tilted sources, may have higher material requirements. The estimated mass is for the film deposition only; additional margin should be included to account for loss during ramp-up, burn-in, stabilisation and ramp-down.

Source:

Distance of source to substrate (in cm):

Material:

- or -
Density of the material in kg/m³:

Multiplier:

Mass for 1 micron layer

Germanium Ge (N-type) Evaporation Process Notes

Germanium Ge (N-type) Specifications

Z-Factors

Thermal Evaporation of Germanium (Ge (N-type))

E-beam Evaporation of Germanium (Ge (N-type))