US 3454370 A
Description (OCR text may contain errors)
United States Patent 3,454,370 NOVEL TERNARY SEMICONDUCTING MATERIALS George Augustus 'Castellion, Stamford, Conn., assignor to American Cyanamid Company, Stamford, Conn., a corporation of Maine No Drawing. Filed May 26, 1966, Ser. No. 553,010 Int. Cl. C01b 29/00; H01b 1/06; H01v 1/20 US. Cl. 23-315 7 Claims ABSTRACT OF THE DISCLOSURE There is provided a semiconducting, single phase composition of matter such as ZnFe Sb ZnCo Sb Zn CoSb MgMn Sb MgCo Sb and FeCd As useful in photocells, thermocouples and rectifiers.
The present invention relates to novel ternary semiconducting compositions of matter. More particularly, it relates to novel ternary semiconducting, single phase compositions of matter and has as its principal object their use in solid state semiconductor devices.
Ternary or three elemental component semiconducting compositions of matter are well known. They find utility in solid state conductor devices, such as, for intsance, rectifiers, photocells, photoconductors, thermocouples and thermoelectric generators. However, many of the ternary semiconducting compounds are unfortunatel found in a plurality of phases. As such, these semiconducting ma terials are substantially ineflicient as thermoelectric compounds used in, for instance, generators. It is further known that admixtures of metals so as to alloy them does not necessarily result in a single phase. Frequently, the new alloy does result in a plurality of phases.
It has been found unexpectedly that semiconducting compounds may be readily formed so as to produce crystals of a single phase. Such compounds can be represented by the formula:
3-m m 2 or A3 D AS where A is an element, such as zinc, manganese, magnesium or iron and D is an element, such as iron, cobalt, manganese or cadmium, m is an integer from 1 to 2 and wherein A and D are dissimilar elements. The compounds prepared by the process of the invention are found to be not only semiconducting, but are found to possess a crystalline habit of a single phase.
In general, the ternary compounds of the present invention can be prepared by comminuting into diminutive particles the elements defined by the above noted formula. In this form, the elements can be easily handled. For optimum operation, the particle size of the elements should not exceed about ten millimeters in diameter. Initially, the elements are mixed in the required stoichiometric amounts, then loaded into a crucible which is evacuated, sealed and subjected to elevated temperatures. This is usually done by placing the crucible containing the mixed elements into a furnace and heating the crucible and contents to a temperature above the melting point of the material or composition of matter to be prepared. Temperatures above about 700 C. will be required to accomplish this end. Depending on the temperature employed, the time required to fuse the elements commencing at room temperature ranges from about thirty minutes to three hours. For most preparations, a time of about one hour appears to be the upper limit.
The temperatures employed are sufficient as to liquefy the elements present. In this state, the elements are intimately mixed by rocking the crucible-containing furnace. Uniformity of product is thereby achieved. Thereafter, the contents in the crucible are cooled at rates ranging from approximately 2 C. to 20 C. per hour and this rate of cooling is continued until a temperature of about 400 C. is reached. At this point, the cooling rate is increased to from C. to C. per hour. Utilizing this technique, which is simpler than the crystal pulling technique normally employed in the art, it has been found that single crystal growth is achieved.
The semiconducting compounds formed by the process of the invention are subjected to several tests to determine their electrical resistance as well as the Seebeck coefi'icient. The latter terms are defined with particularity in United States Letters Patent No. 3,211,517 which is incorporated herein by reference. In each examination of the products resulting from the process of the invention, they exhibit good semiconducting properties.
In order to illustrate the present invention, the following examples are presented merely by way of illustration and are not to be taken as being limitative of the invention.
Example 1 Stoichiometric quantities of zinc, iron and antimony which correspond to the compound ZnFe Sb are admixed in the following manner:
A mixture of 2.176 2 grams of zinc and 3.7180 grams of iron are incorporated in a crucible of quartz tubing and the latter is evacuated to a pressure of less than 1x10- mm. Hg. Thereafter, 8.1057 grams of antimony under a nitrogen atmosphere are loaded into a side arm of the quartz tubing and the crucible is further evacuated to a pressure of less than 1 10- mm. Hg.
The crucible and contents are then sealed and placed in a holder in a conventional resistance furnace. The furnace is equipped with a rocking device so as to permit the crucible and contents to be uniformly admixed. During heating to a temperature of about 1000 C., the furace is continuously rocked. When the latter temperature is attained, it is maintained for an additional 3 hours during which time rocking of the furnace is permitted to occur. Thereafter, the power to the furnace is reduced and the rocking is terminated so as to permit the contents in the furnace to gradually cool at a steady rate from about 850 C. to about 400 C. over a period of about 1% days. Thereafter, all the power to the furnace is shut off and the furnace is allowed to cool to room temperature.
The contents in the crucible are removed and the resultant product recovered is examined microscopically as well as being subjected to X-ray analysis. The product is found to be of a single phase and possesses a resistance of 1 l0 ohm-centimeter and a Seebeck coetficient of 6.5 microvolts/ C. It is also found to possess good thermoelectric properties.
Preparation of the compound ZnCo Sb Repeating the procedure of Example 1 in every detail except that 3.8670 grams of cobalt, 2.1445 grams of zinc and 7.9884 grams of antimony are admixed as elements, on X-ray analysis. Further, resultant compound ZnCo Sb is found to possess a resistance of 1.0 10"' ohm-centimeter and a Seebeck coetficient equal to 11.2 microvolts/ C.
Example 3 Prepare-d of the compound MnMg Sb The procedure of Example 1 is repeated in every detail except that 2.2159 grams of manganese, 1.9618 grams of magnesium and 9.8222 grams of antimony are admixed. Resultant compound is found to be of a single phase and possesses a resistance of 2.0)(10- ohm-centimeter.
Example 4 Example 5 Preparation of the compound MgMn Sb There are admixed 0.9014 grams of magnesium, 4.0726 grams of maganese and 9.0259 grams of antimony in accordance with the procedure of Example 1 above. Resultant product is found to possess a resistivity of 8.0 1O ohm-centimeter and on X-ray analysis is found to be of a single phase.
Example 6 Preparation of the compound MgCo Sb r The procedure of Example 5 is repeated in every detail except that 0.8827 grams of magnesium, 4.2785 grams of cobalt and 8.8387 grams of antimony are admixed. As in Example 5, resultant product is found to be of a single phase and possesses a resistivity equal to 2.0 ohmcentimeter.
Example 7 Preparation of the compound F6Cd AS Repeating the procedure of Example 1 in every detail except that 1.9460 grams of iron, 7.8329 grams of cadmium and 5.2210 grams of arsenic are admixed, resultant product: FeCd As is formed. This product is found to possess a resistivity of 3.2x 10- ohm-centimeter and a Seebeck coeificient equal to 29 microvolts/ C. On X-ray analysis, it is found unequivocally to be of a single phase.
What is claimed is:
1. A semiconducting, single phase composition of matter selected from the group consisting of ZnFe Sb ZnCo Sb ZII COS'bg, MgMl'lgsbg, MgCO Sb and FCCdgASz.
2. The compound according to claim 1: ZnFe sb 3. The compound according to claim 1: ZnCo Sb 4. The compound according to claim 1: Zn CoSb 5. The compound according to claim 1: MgMn Sb 6. The compound according to claim 1: MgCo Sb 7. The compound according to claim 1: PeCd As References Cited UNITED STATES PATENTS 3,211,517 10/1965 CastelliOn 252-62.3 X
OTHER REFERENCES Juza et al., Chemical Abstracts, vol. 61, p. 12733 (1964).
Kasaya et al., Chemical Abstract, vol. 61, p. 15511 (1964).
TOBIAS E. LEVOW, Primary Examiner.
I. COOPER, Assistant Examiner.
US. CI. X.R.
-l22, 134; l36240; 25262.5l, 62.3, 501, 518, 519, 521
UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,454, 370 July 8, 1969 George Augustus Castellion It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:
Column 2, line 38, "furace" should read furnace line 61, "on X-ray analysis." should read it is found that a single phase crystal structure is obtained on X-ray analysis. line 66, "Prepared" should read Preparation Column 3, line 15 "maganese should read manganese Signed and sealed this 21st day of April 1970.
WILLIAM E. SCHUYLER, JR.
Edward M. Fletcher, Jr.
Commissioner of Patents Attesting Officer