US2450886A - Semiconductor - Google Patents

Description

Patented Oct. 12, 1948 SEMICONDUCTOR Charles Alexander Eccoflery, East Orange, N. 3.,

and MadelineDuane Merva, Bernice, Pa... assignors to Federal Telephone and'liadlo Corporation, New York, N. Y., a corporation of Delaware -No Drawing- Application November 20, 1944,

Serial No. 564,408

1 Claim. (or. 175-366) The present invention relates to semi-conductors and particularl to high voltage selenium rectifiers.

It .is quite important for dry type rectifiers, such as selenium rectifiers, that the forward-resistance ls as low as possible and the back-resistance high. The resistance .in the direction of flow is .dependent upon the resistance of the semi-conducting layer, governed to a certain extent by the resistance voltage drop, the trend of the current-voltage curve, of the back-resistance layer,

f and the transition resistancevof the semi-conducting surface to the supply electrode. This transition resistance must be as low as possible and must be independent of voltage if the operationof the rectifier is to be satisfactory. The characteristic resistance curve of the blocking layer itself is dependent upon its chemical and physical composition, and the magnitude of the resistances in both direction of current flow is primarily determined-by the conductivity of the selenium itself.

It has been recognized before that the conductivity of .selenium can be materially increased by a thorough conversion into a crystalline form by annealing it at a temperature close to the melting point and that the conductivity of selenium. can be further increased by the addition of materials, such as pulverized halogen salts of heavy metals, alkalies, carbon powder, or organic compounds. After conversion the additional materials either appear as undecomposed matters having certain conductivity embodied in the selenium, or they are mainly decomposed into oxides or selenides of good conductivity. These latter are conductive bodies and form dangerous .shuntin'gpaths in the selenium and dangerous shunting paths in the selenium,. it.

has been suggested to admix selenium-chloride or selenium-bromide to the selenium and to achieve in this way a better mixture between the halogens and the selenium, the latter being then essentially devoid of conducting residues.

The admixture of selenium-chloride or selenium-bromide brought about an increase in the forward-conductivity of the blockin layer, but at the same time a proportionate increase in the back-conductivity had to be accepted.

Although the later proposal appeared to be another step in the advancement of the art, it did not provide satisfaction in those cases in which it was essential to increase the forwardconductivity of the rectifier without increasing at the same time the reverse-conductivity.

It is, therefore, the main object of the present" invention to add such material to the selenium which not only avoids the formation of conducting residues in the selenium, and also avoids the formation of compounds of selenium with the metallic impurities, but at the same time increases the forward-conductivity of the rectifier without changing its reverse-conductivity, that means a decrease in the relation'of forward-resistance to back-resistance, and allows also higher voltage than achieved before. This main object is achieved by adding one substance of the group of I01, IBr, ICla, IBl'z.

It is a further object of the present invention to provide one substance of the above mentioned group in relation of 100 weight parts of selenium to from .001 up to .5 weight part of the mentioned substance.

It is still another object of the present invention to provide a method of producing a semiconductor for selenium rectifiers which comprises admixing selenium with one substance from the group of ICl, IBr, ICls, IBr: in the mentioned relation. 4

For the achievement of the best possible con ductivity and the highest increase of the forward-conductivity of the semi-conducting layer 4 pound and mix it with the selenium powder, an-

other is to put the halogen compound such as I01 and IBI3, into a crucible, which compound is covered thereafter with selenium, usingthe capacity of the mentioned compound to harden at a tempei'ature slightly -below ordinary room temperature and to change into tumes by heat-- in: up' the crucible. thereby streaming through the selenium positioned above it and mixing invention in connection .with severaldiflerent embodiments. it willbe understood that these embodiments are given by way 0! example only and not as limiting the scope of the invention as 15 set ioxjth in the objects and the appended claim.

What we claim is: In a process for manuiacturin: selenium rectiller elements the improvement that incorporating in the selenium lave: a minor brortion' oi a single substance selected from the class cmsistlna of iodine compounds 0! luorine' s andiodinecompmndsot bromine.

CHARLES ALEXANDER nscommr. mmmmn DUANE mwu ans-nuances cnlm 10 The following references are oi'recordin the tile ol this patent: v

' UNITED STATES PATENTS Number Name Date 2,173,249 Boer et al Sept. 19, 1989 2,226,715 Gelsler Dec. 81, 1940 2,227,827. Dubar Jan. 7, 1941 Waibel Apr. 20, 1943