Making deep power diodes

A process for making a semiconductor device comprising:

• a. selecting a first body of single crystal silicon semiconductor material having top and bottom surfaces which are opposed major surfaces thereof and at least the top surface has a preferred crystal orientation corresponding to the natural solid-liquid facet plane thereof;
• b. vapor depositing a first layer of metal comprising at least aluminum of a preferred thickness on the top surface of the first body and in intimate contact therewith;
• c. placing the first body in an abutting contact relationship with a second body of single crystal silicon semiconductor material having top and bottom surfaces which are opposed major surfaces thereof wherein the layer of metal on the top surface on the first body is in an abutting contact relationship with the top surface of the second body;
• d. heating the two bodies and the layer of metal to an elevated temperature sufficient to form a molten region of the metal of the layer and the semiconductor material of the two bodies in contact therewith, the molten region having a preferred thickness not greater than the value of L which is determined from the following relationship ##EQU5##
• where
• L is the thickness of the molten region in centimeters,
• V is the velocity of the molten zone through the solid semiconductor material in centimeters per second,
• (dc/dt) is the change in concentration of silicon in the molten zone with respect to change in temperature in atomic % of silicon per degree celsius, and
• G.sub.l is the temperature gradient across the thickness of molten region in degrees celsius per centimeter;
• e. establishing a thermal gradient substantially along a preferred crystallographic axis of the first body which is normal to the natural solid-liquid facet plane of the semiconductor metal-liquid surface wherein the bottom surface of the first body is at the highest temperature;
• f. migrating the molten zone through the first body from the top to the bottom surfaces substantially along the preferred axis to form a first region of recrystallized material of a selected portion of the second body having solid solubility of the metal of the layer therein of the second body and to form a second region of recrystallized material of the second body having solid solubility of the metal of the layer therein, the solid solubility metal imparting a selected type conductivity and a selected level of resistivity to the two regions, the first and second regions being integral with each other, substantially free of metal inclusions, and having the crystalline structure of the second body, and
• g. joining together the two bodies of semiconductor material by the integral regions of recrystallized semiconductor material.