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.
Category: Evaporation Sources
Sub-Category: Crucible Liners for E-Beam Sources