Coherent, Inc.

Vg Systems Limited

David C Poole

Arto K Salokatve

An effusion cell (22) including a crucible (28) is configured such that when attached to the MBE apparatus at a predetermined distance from a rotatable substrate holder (24), a longitudinal axis (32) of the crucible is directed toward the substrate holder at an angle to the rotation axis (26) of the substrate holder. The crucible is heatable for melting a material (36) placed therein, the molten material forming a melt surface (38) from which molecules of the material are evaporated. The top of the crucible has an elliptical opening (31), the plane of which is parallel to the substrate holder. The crucible and the opening therein are configured such that a substrate (25) in the substrate holder receives only evaporated molecules which proceed directly thereto from the melt surface, through the opening. The evaporated molecules received by the substrate are contributed from an area of the melt surface which increases in proportion to the square of the distance of the melt surface from the substrate holder, as that distance increases due to depletion of the material in the crucible by evaporation. This provides that molecular flux on the substrate remains constant during the depletion.

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Horsham, United Kingdom

David C Poole