GB768022A - Improvements in or relating to methods of forming p-n junctions in crystalline semi-conducting materials - Google Patents

Abstract

768,022. Semi-conductor devices. GENERAL ELECTRIC CO., Ltd., and JAMES, E. G. Sept. 30, 1953 [Oct. 15, 1952; March 31, 1953], Nos. 8975/53 and 8976/53. Divided out of 723,179. Class 37. P-N junctions are produced in crystalline semi-conducting material by producing, in an inert atmosphere or vacuum, on top of a solid semiconductor body of one conductivity type a molten layer of the semi-conductor material formed at least in part by melting the tip of the body, and then crystallizing the molten layer, which contains sufficient of at least one impurity of opposite conductiv, ity type to ensure that at least the first part of the layer to solidify is of opposite type to the main body. Preferably the original body is monocrystalline and the solidification progressively upward so that the resultant body is also monocrystalline. In one embodiment a monocrystalline slice of N-type Ge 24 is placed on graphite block 25 mounted for vertical movement on a cooled chamber 19 on rod 20 in a chamber 1 through which a current of argon flows, the slice being heated from above by a carbon heating element 7 mounted in watercooled blocks 8 and 9. A thin layer of powdered P-type Ge on top is melted together with a thin surface zone, the P-type impurity being sufficient to ensure that the whole molten mass solidifies from the bottom upwards as P-type Ge when the slice is lowered. The resulting single crystal may be cut into fragments and made into PN diodes or into PNP junction units by diffusion of impurities such as In into the N-type zone. In a second method after part of the molten layer has solidified lowering of the slice is interrupted and powdered N-type Ge added to the Ge remaining molten to give a further N- type layer. Alternatively powdered Ge made N-type by inclusion of As which is more soluble in liquid than in solid Ge, and Ge made P-type by inclusion of B which is more soluble in solid than in liquid Ge are both sprinkled on the body and melted together with the surface zone the relative quantities being such that the first thin layer to solidify is P-type while the remainder is N-type. In all cases blocks of material may replace the powder, or the whole of the molten Ge may be derived from the top of the body, the impurities being added directly to it. The added Ge may also be in liquid form produced by fusion of powdered material in falling through a heated coil on to the body, or melted in separate vessels and poured over the surface. A rod of Ge with axis vertical may replace the slice and after formation of junctions thereon the tip is removed and the process repeated.