The growing of 5 kg single crystals of germanium

Consideration of the factors involved in the efficient production of semiconductor devices reveals the desirability of growing large single crystals of germanium. The technical specification for the material demands that this shall not be achieved at the expense of quality, i.e. the germanium must be of the correct resistivity, lifetime and dislocation density. The realization of the potential advantages has involved the solution of a range of problems. In pulling large crystals the growth must be precisely controlled to give the level interface conditions and thermal gradients associated with good crystal perfection and uniform transverse properties. A high-vacuum radiation-heated furnace is used in which the heaterbaffle assembly is fabricated from high-purity graphite, silica and molybdenum. In this assembly the mechanical construction, the heater and the disposition of the baffle system need careful design to obtain the necessary high-temperature rigidity and the correct heat field over the area involved. (The Crucible internal diameter is 150 mm.) Both stationary and rotating crucible systems have been successfully used, the rotating type having several advantages. Melt preparation demands a high standard of chemical cleanliness, and this is more difficult to attain with large quantities than with small quantities of material. A technique has been developed based on a potassium-hydroxide/hydrogen-peroxide etch which is both safe and completely satisfactory chemically.