US2637770A - Alloys and rectifiers made thereof - Google Patents

Description

May 5, 1953 K. LARK-HoRQvlTZ,.-.T AL

ALLOY AND RECTIFIER MADE THEREOF Original Filed July 13, 1945 May 5, 1953l K. LARK-HoRovrrz Erni. 2,537,770

ALLOY AND RECTIFIER MADE THEBEOF Original Filed July 13. 1945 2 SHEETS-SHEET 2 mVENroR.

17mm/LQ,

Patented May 5, 1953 ALLOYS AND RECTIFIERS'MADE THEBEQF :Karl Lark-Horwitz, Lafayette, and Randall M. Whaley. West Lafayette, Ind.,y assignors to Purdue Research EoundatiomLa-fayctte, 1nd., acorporation of Indiana Original application July `13, I194.5, Serial No. 604,744, now yPatent No. 2,514,879, dated July '11, 1950. Divided and this application December 23, 19518., :Serial No. 66,946

'13 Claims. 1

The present invention relates .to an improvement in alloys of germanium, and more particularly to rectiers `of electricity, which. oier low resistance to current flow in one direction .therethrough and high resistance to vcurrent flow in the opposite direction, made `of such alloys.

In the detailed description of .our invention following hereinafter, it .will be observed that several of the elements which may be .comb-ined with germanium are not metals so that ,the resultant materials are not alloys in .the common meaning of the word. However, for .purposes .of the present disclosure, it is to be understoodthat the word alloy of germanium `as used herein, means to includeaunion or .twoor moreelements, one of which is germanium, and the vother. .or others being metals, non-metals, .or gases, and

the combinationof which exhibits electrical properties such asare found in metals and semi-con- :20 This application formsa division of applicants ductors.

copending Patent No. 2,514,879, granted July 11,

1950, on an application filed July 1,3, 1945, fory tion at frequencies greater than about -5 `megacycles.

;Due to .the aforesaid.defcienciesof these known contact rcctiers, the .art turned to lwidespread use of vacuum tube diodesior rectifying alternating currents. However, Avacuum tube diodes, while overcoming certain of the aiorementioned disadvantages .of the yknown contact rectiers in turnhave the following disadvantages:

1. Inter=electrode capacities which are seriously objectionable Aat high frequencies.

2,. Low forward direction conductance.

3. Requirement of power for heating a cathode.

fi. Require `a large amount of .space as com'- pared 35.0 a ,Contact rectifier.

The germanium alloys of our present invention may .be usedr as the semi-conductors for reetiers of the contact type, which, according voltages 'in the back or high `resistance'direction to one embodiment .of .our invention, possess @the following general .adyantages over known contact reotiers:

1. Ability to withstand continuous operating voltages greater .than -10 volts in the back direction, and some of which are capable of--withstanding voltages in `the back direction of an `order approaching 200 volts.

2. Low forward resistances, lfor example, 30 to 10) ohms at .one volt.

3. High .back resistances, at .about 4 `volts rang.- ing from .about 10,000 vohms to several .megohms e. Maybe used with frequencies .up to .60 megacycles and will still rectify at `3,000 megacycles.

5. Provide rectiers of low capacity ofabout 0.5 micromicrofarads.

6. Less than y5.0% .decrease in peak back y.voltage when ,ambient temperature increases from 23 C( 150.75 C.

7. Do not require power for heating a cathode; and

8. Do not require vmore space than .about that needed" for a commonkone-half watt 4carbon resistor.

The germanium alloys herein disclosedV are all of the class of N -type semi-conductors, i. e., semiconductors which when made into contact type rectifiers present a high resistance to current flow across the rectifying contact when the semiconductor is positive and the contacting metal electrode or Whisker is negative, and a lower resistance when the potential is reversed.

The various germanium alloys of our invention will be described and compared according to the properties they exhibit when made into contact type rectiers. Specific electrical properties hereafter referred to are:

Peak baclc uoZtage.--The voltage-current charteristics measured on rectiiiers using the alloys of our invention show a voltage peak in the back or high resistance direction. This peak generally occurs within a range greater than 10 Volts and approaching the order of 200 volts. It will also appear that all of these rectifiers using alloys of our invention exhibit a negative resistance region in the back direction for currents exceeding the current at the peak back voltage.

Back resistance-In the back or high resistance direction these rectiers have resistances ranging from the order of 10,000 ohms to several megohms as measured at about 5 volts. High resistances are substantially maintained nearly to the peak back voltage.

Forward conductance-The currents passed at one volt in the forward or low resistance direction for these rectiers generally lie Within the range between 5 milliamperes and 40 milliamperes. Actually, somewhat higher currents may be permitted to pass in the forward direction without impairment of the rectifying contact. As will be described later herein, currents greater than 100 milliamperes are sometimes deliberately passed momentarily in the forward direction to produce improvement in certain contact characteristics.

The N-type semi-conductors of our invention comprise germanium having small amounts of one of the following elements or certain combinations thereof alloyed therewith:

Copper and silver of column I of the periodic table;

Magnesium, calcium, zinc, strontium, cadmium, or barium of column II of the periodic table;

Titanium, tin, or lead, of column IV periodic table;

Nitrogen, vanadium, columbium, tantalum, or bismuth of column V of the periodic table;

Chromium or uranium of column VI of the periodic table.

Cobalt, nickel, or palladium of column VIII of the periodic table.

N-type semi-conductors of germanium may also be formed by alloying small amounts of, for example, phosphorus, arsenic, or antimony with germanium, but in rectiers using such semiconductors it has been found that excessive currents pass at voltages greater than about 3 to 10 of the volts in the back direction which permanently injure the rectifying contact. It will be understood therefore that our present invention only relates to semi-conductors of the N-type which exhibit high back voltage characteristics in excess of at least l volts, and does not concern all N-type semi-conductors consisting of an al loy of germanium, as for example, the group last referred to.

Other features and advantages of our invention will appear from the detailed description.

Now, in order to acquaint those skilled in the lil art with the manner of making alloys in accordance with our invention, and the utilization thereof as rectiers of electricity, we shall describe in connection with the accompanying drawings and the tables following hereafter certain of the processes used in making the alloys which lie within our invention.

In the drawings:

Figure 1 shows the voltage-current characteristic curves of several rectiers using certain of the alloys of our invention, which curves are not to be taken as typical of given alloys but merely to represent the type of characteristic exhibited by such alloys in general.

Figure 2 is a graph illustrating the electrical characteristics of rectiers using different types of surfaces on one alloy of our invention.

Figure 3 is a sectional view of a rectier, the semi-conductor of which comprises an alloy of our present invention.

Each alloy represented by the curves of Figure 1 is designated by a code number. The latter part of each code denotes the amount in atomic percent of the particular element or elements added to germanium to produce that alloy. No atomic percentage figures for the addition of nitrogen to germanium are given since it is diilicult to determine accurately the amount or number of nitrogen atoms alloyed with the germanium.

In the following Table I there are set forth minimum, average, and maximum values of peak back voltage and forward current obtained on rectifying contacts using certain germanium alloy which we have made in accordance with the general procedure to be described later. The amount of the added element alloyed with germanium is set forth for each melt in atomic percent, i. e., the proportionate number of atoms in percent of the elements added to the total number of the atoms of germanium and added elements present. For purposes of adequately setting forth and claiming our invention, these additions to germanium are to be understood as being included in the term Group A used hereinafter. Substantially all melts in which the addition consisted of a single element made to date in accordance with our invention are contained in Table I. It will be observed from that table that a large number of melts with certain added elementsv were prepared and it will be understood that the results given are the average results of all of the melts in each instance. It is to be understood, however, that the spread or range of Values given in connection with each of the elements added to germanium might not be true for any particular melt of such addition agent. Characteristics for rectifying contacts on any given alloy will lie somewhere within the range given. Further, all points on any given alloy listed in Table I and Table II, referred to hereinafter, will not exhibit the same electrical characteristics. Points may be found on each of the alloys disclosed at which the peak back voltages, back resistances, or forward currents lie in the lower regions of the ranges given above for these values. Also on the same surface of each alloy other points of contact may usually be found with electrical characteristics which lie toward the upper limit of the ranges above set out. However, as will later be discussed in more detail, some of the alloys are of greater uniformity than others with respect to rectification characteristics.

tor melting, the 'furto be independent of IThe germanium is melted in lents are disposed furnace. Alloy'inggermanium with nitrogen .may

mosphere of nitrogen which may be either puried nitrogen or nitrogen direct from a comnitrogen at `pressures ranging from about'2`mm. to '760 mm. -Hg at a temperature of 1000" to 1050 C. Groodv results appear pressurev and melts prepared within the above range of pressures were all satisfactory.

The germanium ksuccessfully used for these/alloys hadV .purity approaching .100 .and electrical germanium which We have successfully alloyed with other elements to form .the alloys listed in phere of helium. Precaution should 'be taken to prevent 'the accidental .introductionof unknown from sources such as thecrucible or vlooa't'in which the Iingred nace itself, o'r some material volatilized in the mercial cylinder.

o be eiected by melting the `germanium in an at- 50 resistivity greater thanaboutone ohm cm. The

ammiro' 05000500550 t X wl 222442.23222 no) nu B S l ...sa .t u.. h I 1.. up 5 .055 5 C mm W l .MUNI lmlmmw mvm i WOW i ,78 55051127757 D m 1 F0 5, 5.a. `55 55.50 0 ab X 2 20 m23w7319mm8 vw klo. 0 00 55050 005 CV W 55 71324mw586w a( A wm 3a .u 50 55035500005 E 1 1.2 2 211212232 P M Tables I-.andII was prepared yfrom GeOz obtained from the vlilagle-Pioher Lead `Company .of Joplin, 60 55 Missouri. The oxide was reduced in an atmosp'here of commercial hydrogen at temperatures of 650 to`700 C. over a period of three to four hours. The oxide reduced in this manner leaves ig the germanium metal in the form 4of .a gray- 35 60 green -powder Whichis .then alloyed with another element' or elements in the manner and proportions described.

The aforesaid melts ci germanium and Ythe added element or elements were heldin the molten 65 state long enough to allow mixing of the constituents, and it has been found thatabout 5 to minutes is suicient for this purpose. Usually ingredients `to form melts of about live Lto six mamar/.a

TABLE .I

Additions to' germanium [In atomic percentl] Addition and percentages ne; .40, 1301.0, .201.25, .70, .28, .20, .31, 2.0, 2.3, 2.3, .02s, .20, .80, .10,

.40, .20, Cd: .90, Caz-*2.0 1.35

Ni: 1.25, .10, .50, L0, 1.0,1.0,1.0,1.0.. N2: solidified in N2 at pressures of 2. 18, G00, and 760 mm. Hg. Pd: .50, .50

rward Current at one volt" (Milliampei'es) ,8.5555698582.09003076651238 r1|.-l-l 11 1111 1 Peak Back Volt- F0 age (Volts) Min.l Ave. Max. Min.. Ave. Max.

In Table' II below there are .setorth-the melts in which two elements have` been alloyed with germanium. The additions of these Ycombinations of elements are also set forth in atomic percent @e and .perhaps detrimental impurities into the melt TABLE I1 M ets of more than one addition to. germ [In vatomic percent.)

additions and Percentages as previously defined. .It will be understood that the alloys 'set forth in this table are also. to be includedin the term Group A above referred to at one Volt of rectiers made of these alloys Aarealso set forth in this table.

for purposes of claiming our present invention. The peak back voltages and the forward Icurrents Ca, l0 Sn, .40 Ca r1 TTTTT ,CCSNPPLBBLNUBOOOO 1..\.0000U00000000022U0( 0 :2000555555555 .3 .nooo

grams each were used in proportions above set forth in detail. After the constituents .had been Thegermanium alloys of our invention maybe allowed to mix, the melts were allowed to solidify prepared in all :cases except for'the'germaniumand 'cool which was accomplished ,either vby imnitrogen alloy, by melting lpure germanium' with mediately removing heat or by controlled Vcooling the desired alloying element or combination of apparatus. In certaincases theuniformityof the elements in eithera high vacuum of the order'of 75 melt is `aiected by the manner in which it is amounting to milligrams or about 0.8 atomic percent of tin.

The crucible and contents were then placed inside a graphite cylinder used as a heater in the high frequency eld of an induction furnace,

and lowered into a vertical quartz tube which was then evacuated and maintained at a pressure of about 10-5 mm. mercury. Power was then applied to the external coil of the induction furnace to melt the germanium and hold it molten for about 5 minutes. The melt was then allowed to cool by merely turning off the power to the coil. Thereafter wafers were cut from the alloy, and were soldered with soft-solder to a suitable metal electrode to produce a very low resistance non-rectifying contact with one face of the wafer. The exposed face Was then ground with 600 mesh alumina and etched for 2 minutes with an etching solution consisting essentially of HNOS, HF, Cu(NO3)2 and water in proportions to be later described herein. These wafers were then assembled in suitable cartridges each provided with a conventional metal electrode or whisker which was used to contact the alloy surface. Across the rectifying contact thus produced We obtain the electrical characteristics described above.

As mentioned in the above specic example, C

the surfaces of these alloys are usually ground flat and then etched in a manner to be described in detail. However, as hereinafter related, the etching of the alloy surfaces is not essential since, for example, by breaking open a melt, points may be found which exhibit the aforementioned electrical rectifying characteristics. Such broken surfaces present geometrically irregular faces which introduce some difficulty in assembly of the rectiers. at and etching it appears to be the most feasible manner of producing the rectifiers in the commercial practicing of our invention.

From the above Table I it will be observed that the majority of experimental work conducted in the development of our invention has been with the alloy germanium-tin. In connection with our experimental work with tin it has been found that above 0.1 atomic percent of tin content, the amount of tin added is not critical. Gerinanium' containing above about 0.1 percent tin usually shows tin separated out, both at internal grain boundaries and on the outer surfaces. In some melts containing tin in excess of 0.1 atomic percent, ductile layers of this tin-rich material were frequently observed, particularly in the lower regions of the melt. In this connection we wish to observe that in making the germanium-tin alloys it is desirable in producing the melt that the boat or Crucible in which the elements are contained be gradually removed from the hot furnace region. This will produce more uniform alloys, particularly if the melt is so removed that the top region of the melt is the last part to cool. It appears that germanium becomes saturated at about 0.1 percent tin under the melting and cooling conditions used. However, in our experimental work larger amounts of tin were added in order to observe if such solubility depended upon the amount of tin available; more tin merely Thus, grinding the alloy surface l segregated. At 17 atomic percent addition of tin, the entire melt was interlaced with tin-rich veins which had metallic low resistance ohmic conductivity.

With bismuth additions it is difficult to control the amount of bismuth actually remaining in the germanium during the melting cycle. A considerable fraction of the bismuth volatilizes so that quantities added have little relation to the quantities actually remaining in the melt. However, the results indicated in Table I in connection with bismuth were obtained by the addition of bismuth to the extent there indicated.

After the melts have been made as above described they are suitable for use as rectifiers of electricity by simply making contact with the surfaces of such alloys with suitable electrodes or whiskers. In most of our experimental work a 5 mil tungsten Whisker sharpened electrolytically with a tip diameter of less than 0.1 mil was used as one electrode or whisker, the other electrical contact usually being made by soldering the alloy to a suitable conductor. However, tests have shown that the peak back voltages of rectiers made from the alloys of our invention are little affected by the metal of which the Whisker is made. Whiskers made of the following metals have been tried and only Very slight deviations were noted over a large number of points of contact with the alloys of our invention: Mn, Pt, Ta, Ni, Fe, Zn, Mo, W, Au, Cu, Ag, Zr, Pt-Ir, and Pt-Ru. It appears therefore, that choice of a Whisker material may be determined on the basis of requirements other than the peak back voltage on rectiiiers using the alloys. These electrodes or whiskers may have Contact with the surfaces cf the alloys as formed upon solidification, or on surfaces exposed by breaking the melt. As mentioned above, however, it is desirable to grind and etch the surface. Thus in one method of producing rectifiers using the alloys of our invention, the melts, which usually were of pellet form 5 to 10 millimeters thick, may be cut into thin plates or slabs and a surface thereof ground with a suitable abrasive such as 600 m'esh alumina (A1203). The abrasive used is not critical in that it has been found that other abrasives such as CrzOa, MgO, VazOs, SnOz, ZnO and 40 paper are equally satisfactory. This may then be followed by a further grinding step with fine emery paper although this grinding step may be eliminated, if desired, without substantially altering the nal product. The surface of the plate or slab is then etched with a suitable etching solution which in one modification of our invention has the following approximate composition:

4 parts by volume hydrofluoric acid (48% reagent) 4 parts by volume distilled water 2 parts by volume concentrated nitric acid 200 milligrams Cu(NO3)2 to each 10 cc. of solution.

Such a solution will satisfactorily etch the surface of the plates or slabs in about 1 to 2 minutes at room temperature and may be applied with either a swab or by immersing the surface in the solution. This etching is not particularly critical but care should be taken not to unduly extend the etching since then a high polish is produced which may impair the performance of the alloy.

We have also found that other types of etches may be used effectively on the germanium alloys ace-mm,

9', ofi our inventioniin' addition to the etchingfabovc'- described. Modified etching solutions a-nd procedures are as follows:

A*r solutioir consisting approximateiy" of' 1' gram` stannyl chloride' in` 50 cc: off l- Of may" beused' as an elcctrolytic bath' for etclii; fthe alloy sur faces. Immersing the alloy as the anode-'in'tl'iis solution will result in satisfactory etchingwi-tiiin aboutV lil/"2 minutes at about' 21212- volts applied.

An' alternative modification' of an eiectrolytic etcliing solution may comprise 5" parts con'cen`- trated HNOaand 5o *parts H2O by 'voi'u me; Using i'flie alloy as the anode for 'about` minutes at l' to 2 volts willi resultin a satisfactory' etclti;

Reference may now be` hady to Figure 2": ofi the drawings illustrating the effect' of' etchingofionelof'fthe'alloys of' our invent-ioni, 'lie-alioyl selected to illustrate the effect of etching is iden'-n ti'ed afs'- melt 24 P'f-OUlSGf-.Zsn This-- melt as' appears-- from the aforesaid designation consti-- tutes .25* atomic percent tin. The curve identi# ieol'A byy reference numeral E illustrates theu elec'- trcal" cl'i'aracteristicJ of the gerrnaniumtin` alloy above identified in whiohtiie surface wasground1 with`- 600'" All'gGiry but-not etched. Tirecurve indicated byt the'v4 reference numeral 2v illustratesVA the electricalf cha-racteri'sticsl which wereobtainedf'4 onay freshly broken surface of any alloy of thealcove` composition but' which surface has notbeen etched; ('urve-l member S'illustratesftlie-elieetrii call characteristic ot'a surface groundf-with` 600-L AilzGr and tli'en'A etched in accordanceV with trie-4 manner first described.

The curve indicated the reference' numeral 4f illustrates electrical" characteristics of' anotherl pointA on the alloy' afteretciiingl as descriledirr connection with curve-3; the-'curves' ti and representing the best and poorest performances; ree spectiveiyy ofthe particular' germanium tinalloy aboveA identified; afteretching; it' is tube olon serve-slthat inxv this` graph the voltagev scale in: the forward direct-ion i'sthere' expanded' by' a factor of' 10 asVv comparedy to the voltage" scale indicating'the high'V back voltage characteristics' ofr'the alloys'` of our invention: As indicated; the currents are given in milliamperes.

It will be observedAt from arr examination of' Figure-'1.2i thatl trie electrical' characteristics ofL av rectifier usine; broken' surfaceL exhibit" high'n back: voltages: andi forward? conductances within the range of values obtained when using' al ground and surfacei However, such breiten'V surfaces" are shiny' and'v geometrically ire regular" so that" the Whisker tends to' sind@whichy is'l undesirable in: assembling permanent rectifier units.. From: Figure 2 it' is apparent" that the high back voltage'and l'iigh ba'ck'resistanceprop orties are inherent in" the'A alloys and? thatthe etching: is effective for' restoring such properties afterrgm'nding. Further, we-have' discoveredthat" natural? surfaces formed when' soiidifying thel alloys in vacuurd will; if' not contaminated or" otherwise affected by grinding,` give iiiglif liaclri' voltages and high bach" resista-hoes when" mountedi and testedi' in air;

For certaiir appiicationsof'v these' rectiiier's" it? is desirable thatzi they have back'` resistanoes ex"- ceedng oneinegohm ataicout 5 volts'. Usingl theproce'dure described above will cocasionailyy produceL sucht high back resista-nues; However," we havelfound that ar` substantial i and-I perman'entf in crease in the back resistance can be effectedfby applying power overloads across the Contact, for shortrintervalsoff' ime; eachl ofl'ength about 1/4', tor.J 1i secondA orf longer; The power treatment* can" 10 heteffected-y with thec use of either' alternating ori direct corren-tiv gradually' increasing the voltage'appledi and'ihence thecurrenttpassed oy the contact-during successive pulses, anv optimum value can bel foundi toproduce the maximum back resistance for a given contact. For'idirect-y current treatment in the forward direction such optimum current valuesrange from about 200 toV 800I mil-li-amperes; For` alternating power treatmentgthez optimum values of forward peak current range: from;` about 300 milliamperes to 1000 milliamperes. One can apply such alternating current treatmentsimply by connecting the rectifier in serieswith acurrent limiting resistance and the secondary of a transformer. Dependingupomthecsizefof this current. limiting resistance,.values of.A 10 to 40 ohms have been.

used; voltage pulsestranging from 7 to 60 volts across'. the 'rectiert andlresistance' servel to' yield the maximum l increase back. resistance.

Table III shows the permanent' effects'ofsuch` power;l treatmentv upon. ar. few. typicalV rectiers'v using'alloys ofl our invention` and prepared as describedi measured at abouti 425 volts.y

50 times the va'luesmeasured before" treatment;

Relatively minorincreasesv of" 1'0'to 20percent'are efectedon the. pealcbachvoltage. Forward ,cur-

rents' atv one volt' are inl generali decreased.,

amountsfrrangingifom 10 toz- 5I0`percent.

TA 'BL IIIVV Eafe'cnr-` of? power treatmentA [Values beforeepowerf'trcamnent arcillowed'in parentheses'by` valuesafter-powentreatmeuti] It"'las= been4 demonstrated" above that the high baclr' voltage;- highf la'cli resistance, and good forward? conduct"ance'properties7 disclosedare in` herent in the germanium alloys of" our invention.`

Modifications of sur-facei treatments# or powerv treatments as'describedabove'v-will; however; vary y 1 the*magnitudeffof-tliese ipropertiesy withinI certain general limitsa For" example, on a'L given alloy surface; variations insurfacet'reatment' and" power' treatment may be expected' toA vary the average peak' baclvoltage y-a factor of'abouta;

i tlieraverage-'forwardicurrent bya factor ofv about 2, anditheaveragebacir resistance by factorsupv to.' 50. It? willi be? noted thtftheback resistanceis Itlwill be seen from the table tirati the most-significant?L effect ofthe power treat ment is the increase. inrthebaclrresatance as This resistance: i`s increased by factores ranging. from. about. 10i tok -11 conducted under our invention, the approximate figures of the minimum, average, and maximum values of peak back voltage and forward current at one volt which might be expected on the germanium alloys consisting of the addition of a single element.

TABLE IV Peak B ack Voltage Foggefutent Alloy (vous) (miuiamperes) Min Ave Max. Min. Ave. Max.

25 75 150 2 15 30 2U 80 160 7 1 0 25 25 75 1 50 5 1 5 25 25 75 1 50 5 1 0 25 50 90 7 1 5 30 50 100 5 1 2 2O 25 70 13 5 1 1 5 25 65 11 O 5 1 5 25 10 50 100 2 10 20 20 50 10 5 5 1 2 1 5 15 50 125 7 1 3 20 15 40 100 10 1 5 30 25 40 80 7 10 20 1 0 30 70 3 7 15 20 30 3 5 10 1 5 20 20 40 70 3 1 5 30 l 5 40 75 l 5 10 1 5 25 40 5 1 5 10 10 25 65 10 25 40 20 25 50 2 5 20 It will appear from the above table that the ranges of values for the better alloys appear to be quite similar. Differences enter in the manner in which the values, within the ranges indicated, are concentrated.l For example, the nitrogen alloys can usually'be expected to have '70 to 90 percent of back peak voltages over 60 volts. Values on tin melts are more uniformly spread within the range of the limits given above. For the tin melts approximately of the points on the surfaces thereof will have voltages above volts. It appears that the pure germanium alloyed with tin or melted in an atmosphere of nitrogen represents the most advantageous alloy. Following them, alloys of pure germanium with calcium, strontium or nickel appear to be in order. It is to be understood, however, that one skilled in the art working Within the range of the alloys herein disclosed will readily be able to produce alloys having high back voltage and resistance characteristics and good forward conductances.

In Figure 3 of the drawings we have shown one type of rectifier in which our invention may be embodied. In the form of the device there shown a wafer 5 which may be of any of the germanium alloys above disclosed is mounted to have a low resistance non-rectifying Contact with a metal electrode member 6. An electrode or whisker 'l is connected at one end to an electrode supporting member 8 with the end of the Whisker in contact with the surface of the germanium alloy wafer 5. The standard 9 provides for mounting of the members supporting the wafer 5 and electrode or whisker 1 in insulated relation. The rectifier contemplated by our invention may be of various forms, the only critical constructional feature being that the germanium alloy wafer comprising the semi-conductor, and the Whisker for contacting the surface of the wafer being arranged and supported so that one end of the Whisker engages the semi-conductor surface. It is understood that suitable leads are connected to the wafer or semi-conductor and to the Whisker or metal electrode so that the device may have application in any desired circuit for use in the rectication of current.

While we have disclosed what we consider to be the preferred embodiments of our invention, it will be understood that various modifications may be made therein Without departing from the invention.

We claim:

1. An electrical device comprising a, semi-conductor, a counter electrode having substantially point contact with said semi-conductor and a second electrode having an area of Contact with the said semi-conductor which is large compared to that of the counter electrode, said semi-conductor comprising an alloy of germanium having a purity of the order of 99% in combination with nitrogen to provide a device having a peak back voltage in the range in excess of 10 volts and approaching the order of 200 volts, said alloy being one as made by melting germanium having a purity of the order of 99% in an atmosphere of nitrogen at a pressure of about 2 mm. to '760 mm. Hg, at a temperature of about 1000 C.1050 C. for about 5 to 15 minutes.

2. The method of making an electrical device which comprises melting germanium having a purity of the order of 99% in an atmosphere of nitrogen at a pressure of about 2 mm. to 760 mm. Hg, at a temperature of about 1000" C.-1050 C. for about 5 to 15 minutesy solidifying the melt to form an ingot, and cutting from the ingot formed upon mass solidication wafers to which contact electrodes may be applied.

3. The method claimed in claim 2 comprising the additional steps of grinding the severed Wafer and then etching the ground surface to provide optimum contact points for contacting electrode members.

4. The method claimed in claim 2 comprising in addition the step of etching a surface of the semi-conductor wafer which is cut from the ingot.

5. The method of claim 2 comprising the additional step of etching a surface of the semi-conductor Wafer out from the ingot in a solution in approximately the portions of 4 parts by volume of hydroluoric acid (48% reagent), 4 parts by volume distilled water, 2 parts by volume concentrated nitric acid and 200 milligrams Cu(NO3)2 to each 10 cc. of solution for a time period in the general range between 1 and 2 minutes.

6. An electrical device comprising an alloy of germanium having a purity of the order of 99% and nitrogen, and a pair of electrode elements in contact with said formed alloy, one of said electrode elements having substantially point contact with the said semi-conductor and the second of said electrodes having an area of contact which is large compared to that of the point contact electrode, said alloy being one as made by melting said germanium in an atmosphere of nitrogen at a pressure of about 2 mm. to 760 mm. Hg, at a temperature of about 1000o C. to 1050 C. for about 5-15 minutes.

'7. The method claimed in claim 2 comprising, in addition, securing an electrode element to one surface of the out Wafer, locating a second substantially point contact electrode upon a different surface of the cut Wafer and in substantially point contact therewith, and then applying electric power between the electrodes and the semiconductor.

8. 'I'he method claimed in claim 7 comprising, in addition, regulating the supplied current to the forward direction through the cut wafer and limiting the current value to the range between 200 and 800 milliamperes applied in pulses of between 1A; to 1 second in length.

9. The method set forth in claim 8 comprising, in addition, the steps of connecting the formed device in series with a current limiting resistance and a secondary of a transformer of alternating electric currents controlling the peak current in the forward direction to the order of` between 300 and 1000 milliamperes so that the voltage across the rectifier and limiting resistance is of the order of between 7 and 60 volts and the limiting resistance is of the order of 10 to 40 ohms and regulating the period of application of the alternating current to intervals varying between 1/4 and l second in time duration.

10. An electrical device comprising a semi-conductor, a counterelectrode having substantially point contact with said semi-conductor and a second electrode having an area of contact with said semi-conductor which is large compared to that of the counterelectrode, said semi-conductor consisting of an alloy of germanium of the order of 99% purity and nitrogen to produce a device having a peak back voltage in the range in excess of 10 volts and approaching the order of 200 volts, the back resistance of said formed device being of the order of between 10,000 ohms to several megohms at about volts and the forward current being in the range of between 5 and 40 milliamperes at one volt in the low resistance direction of current now through the device, and said alloy being one as made by melting said germanium in an atmosphere of nitrogen at a pressure of about 2 mm. to '760 mm. Hg, at a temperature of about 1000 C. to 1050o C. for about 5-15 minutes.

11. An electrical device comprising a body of germanium having a purity of the order of'- 99% in combination with nitrogen, and two electrodes in contact with said body, said body being an alloy as made by melting said germanium in an atmosphere of nitrogen at a pressure of about 2 mm. to 760 mm. of Hg, at a temperature of about 1000 C. to 1050o C. for about 5-15 minutes.

12. An electrical device comprising a body, a first conductor in contact with a part of said body, and a second conductor in contact with a 4different partA of said body, said body having at least a portion constituted of a germanium base alloy, said alloy having nitrogen as a minor constituent, and said germanium having a purity of the order of 99%, said alloy being one as made by melting said germanium in an atmosphere of nitrogen at a pressure of about 2 mm. to 760 mm. of Hg, at a temperature of about 1000" C. to 1050 C. for about 5-15 minutes.

13. An alloy of germanium and nitrogen as made by the process of melting germanium having a purity of the order of 99% in an atmosphere of nitrogen at a pressure of about 2 mm. to 7,60 mm. Hg, at a temperature of about 1000 C.- 1050 C. for about 5 to 15 minutes.

KARL LARK-HOROVITZ. RANDALL M. WHALEY.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 2,446,467 Fry Aug. 3, 1948 2,447,829 Whaley Aug. 24, 1948 2,505,633 Whaley Apr. 25, 1950 2,514,879 Lark-Horovitz et a1. July 11, 1950 2,530,110 Woodyard Nov. 14, 1950 OTHER REFERENCES J. A. C. S., V01. 52 (1930), pp. 5160-64.

Claims (1)

1. AN ELECTRICAL DEVICE COMPRISING A SEMI-CONDUCTOR, A COUNTER ELECTRODE HAVING SUBSTANTIALLY POINT CONTACT WITH SAID SEMI-CONDUCTOR AND A SECOND ELECTRODE HAVING AN AREA OF CONTACT WITH THE SAID SEMI-CONDUCTOR WHICH IS LARGE COMPARED TO THAT OF THE COUNTER ELECTRODE, SAID SEMI-CON-

Images