US2615966A - Alloys and rectifiers made thereof - Google Patents

Description

9ct. 2s, 1952 K. LARK-HQROVITZ ETA L ALLoYs AND RECTIFIERS MADE THEREOF 2 SHEETS-SHEET 1 Original Filed July 13, 1945 Oc. 28, 1952 K. LAK-HoRovlTz Erm. 2,615,966

ALLOYS AND RECTIFIERS MADE THEREOF' 2 SHEETS-SHEET 2 Original Filed July 13. 1945 S Si Patented Oct. 28, 1952 UN ITE-,D STATES PATENT I(B125F11(11?.

.ALLOYS AND RECTIFIERS MADE THEREOF Karl LarkJ-Horovitz and ,Randall .M. fWhaley, La Fayette, Ind.,-assignorsV to Purdueltesearch "Foundation, La Fayette, In'd., a corporation of Indiana 'Original application July 13, 1945, Serial No. 604,744, now Patent No. 2,514,879, ydated July '11, `1950. Divided and this application December 29, 1949, Serial No. 135,746

This "application isa Vdivision 'of application,

ySerial 'No. 604,744, illed July 13, y1945, now lPatent No. 2,514,879, issued July 11, 1950.

The present inventionirelates` to van improve- Vment in valloys of germanium, Vand'more yparf Jticularly torectiers .of velectricity, which offer -low resistanceto current flowin one direction therethrough'and highresistancelto,current iiow l,in '.the opposite direction, :made 'of f such Lalloys.

In the detailed :description iof our .invention followin'g hereinafter, .it will .be iobserved that vseveral .of the elements which ymay be combined `vwith germanium are notfmetals so that Athe resultantrmaterials are notaalloys in the com- .mon `meaning of .the word. However, for purposes of the present disclosure, it isto. be understood that .the word alloy of germanium as Aused'herein, means to .include a union of two Hor'rnore elements, one 'ofwhich is germanium,

'and the other vor "others `being Ymetals, nonmetals, or gases, and the vcombination of which exhibits electrical properties such as are found in metals andsemi-'conductors- The known' contact rectiersy i. e., rectiers comprising suitable metalelectrodes,v and' afsemi- Vconductor fhave at fleast v'one kof the following disadvantages:

.1. Inability to withstand in ycontinuous `use voltagesin the back or high'resistance direction greater-.than about 10' volts-without permanent injury .to the rectier.

.2. Inability .to pass suicient current in .the

for-ward direction .forsatisfactory operation Vof A"associated apparatus.

`3..Low back. resistance prohibiting use of the Vrectiiier in high'impedancecircuits, that is, circuits Aover about 100,000 ohms.

4. Seriously decreased eiiiciency in rectifying at frequencies greater `than about 1 to 5 megacycles.

v5. Capacity too high to 'allow' e'iicient oper- =-ationat frequencies greater than about 5 megacycles.

Due` to the aforesaid deficiencies of these known contact rectiers, the art turned .tolvwdeg 15 Claims. (Cl. 175-4366) the following general `advantages over .known contact rectiers:

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

2. Low forward resistances, for example,.30 to 100 ohms at one volt.

'3. High back resistances,:atfaboutl voltsrang- 'ing fromV about 10,000 ohms '.to'several megohms.

4. Maybe used withffrequencies upfto .60' megacycles and willstillfrectify at 3,000/megacycles.

5. Provide rectiers of low capacity'of.v about 0.5 micromicrofarads.

6. .Less than 50% decrease in peakzback ',-voltage whenambient temperature increases `from 4.23" C. to 75- C.

7. Do not require power for heating acathode; and

8. Do 4not require .morespace 4thanabout vthat needed for a common ene-half watt carbon resistor.

The germanium alloys herein disclosed .are al1 of the class of N-type semi-conductorsi e., semi-conductors which `when made into contact type rectifiers-present ra highv resistance to current flowacross the rectifyingfcontact whenhthe semi-conductor 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 back voltage: The voltage-current characteristics measured on rectiers using the alloys of our invention show a volta-ge peak in the back or high resistance direction. This peak generally occurs within a range greater than 1f) volts and approaching the order of 200 volts'. It will also appear that all of these rectiiiers using alloys of our invention eX- hibit 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 or the following elements or certain combinations thereof alloyed therewith:

Copper and silver of column l 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 of the 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.

of germanium, as for example, the group last referred to.

- Other features and advantages of our invention will Iappear from the detail description.

Now, in order to acquaint those skilled in the art with the manner of making alloys in accordi 4 ance 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 l shows the voltage-current characteristie curves of several rectiiiers 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 rectiiiers usingV 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 l 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 iigures for the addition of nitrogen to germanium are given since it is difficult 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 alloys 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 elements 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 or" the elements added to germanium might not be true for any particular melt of such addition agent. Characteristics for rectifylng 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,

'-In Table II below there-are -set`forth'i'the melts in which .two elements have been alloyed'vvith germanium. The :additions lof these combinati'ons of elements :zare alsof4 set lforth zin nato'mic Ll:percentil-as previously; defined. x It willbexunder- 'stod that the :alloys set forthin v.thisztable are 'z'referred'tolfor purposesot claimingf our present ;.invetion. The peak back'volta'ges' and the-forifward `:ci'irrents at .zonet volt of 'rectiersl'made c of these alloys are also set forth in thisitable.

. 'Melts of .morezhjanj oneadditiontofgermaiiium [111 atomic per cent-:.1v

f of f1 0"51lmm.srnercury.-atiabout1000C5for invia-n :atmosphere of helium. 'Precaution i should ybe taken'lto preventi'the'accidental intrdu'ctionff unknown `and -`pe'rliaps detrimental .impurities into fthe melt *fr-omi sourcessuchf as the "crucible or boat in which the ingredients are disposed 'T for. v"melting, "theil furnace itself, `or 'some lmaterial volatilized in 'the furnace. Alloyin'g Y germanium with' nitrogen fmayfbeeffected by melting''thefge- Ymaniurn in an atmosphere f `nitrogen fW- liich '-maybe'either'purie'd' nitrogen or nitrogen direct from a commerciali cylinder. *The germaniumf'is Yrituel-ted in nitrogenat 'pressures/ rangingdrm :ab'oiit'l Zmm. `to 760i mm. 'Hg1 'at-a temperature' f 1000to'1050 C. Good resultsfappear't `-belin'cie- .the above'range ofv pressures Werefallsatis actory. `The5germaniumsuccessfully used fori-ches falloyshad purity5approaching 10 0 ,l and-electrical resistivitygreater'V than-aboutone ohm cm. "The f germanium iwhich 'we have i `successfully valloyed lv'vi'thfother elements" to 'form theV alloys listed in Tables 1I and II was fprepared from A'G eQz vobtained Vfrom the EagleiPieher `Lead Company `of Joplin, Missouri. The oxide was reducedA 'inI an atmosphere of commercialfhydrogen at temperatui'es vof 650 vto 70W-C.v over "a, period'of 'three Ito four hours. 'Theoxide reduced ini this manner leaves i the'v germanium `'metal in `the iiorm f fa "'grayfgreen powder "vvhich is thenalloyed vvith -'ano'ther element' orf elements: inthe mannerfand 'proportions described.

The aforesaid melts of germanium "andffthe added element lor elementsj-"were'-held the jmlten state Y` 'long enoughj to allow mixirig 'of e constituents, land 'jit "has "been found that `v"ja-b i`n`ut"5 13 015V` minutes' is s u'iiicieni', v for 'this purfpose. Usually ingredients to form Ameltsjo'i l about 've 1'to'jsiii grams" each Were used inipropotions above setfforth in detailv tAfter the constituents had 'beenallowedto mix,"t he meltsvvereffallowed lto lsolidify and/ cool v"which was accomplished (either by immediately removingheat or"`by;con trolled coolingfap'paratus In certain c a'sesfthe uniformity of 'the"m e1t`isjaiectedlbythe manner `in Whi'ch'jit is cooled. yThese"variation-s 'willlbe or"discussed later.

l IvA' specifici meltjin' accordance with our invention :was'preparedasfollows:

Pure GeOzA Wasreduced'in hydrogen atatnospheric pressure for about three jhoursi'at 650"to 700 C. Six'grams'ofjpuregermanumpowderso obtained werethen placed in`v aporcelain 'crufJL l' ble together with Vsmall flakes ofV pureftini amount- *ing toSv 25 milligrams ".orabout 018atom'ic percent TheV ACrucible and *contentsfwere "then .placed inside a l graphite fcyiinder 'used'.fas." a =ha5erin ihefhigh frequenyneid ofeninuuciienfnce,

and lowered in'aL vertical quartz'tube .Whih J was thenfevacuatedand maintained at'a'jpressure of a'il0o1'it"1 f)-'5 mm. "'^mercury. "Powerr Was' ..then.ap 'fp'lied to the external coil .ofv'fthe, inductionfur- @naee'to meltthe germanium and'hold itfmolte-n 170 'ioraboui 5 minutes. .The m5151525 tnenauowed `VAto 'cool 'by' merely fturning...off .thefpower to the coil. Thereafter Waferswere cutfrom thef alloy, andl-weresol'dered with softfsol'derto aasuitable metal lectrode Ito '.projduce .a l .very '.lowres-istance'r non-reeiifying Contact with one 'farce 'of the wafer. The exposed face was then ground with 600 mesh alumina and etched forf2 minutes with an etching solution consisting essentially of HNO3, 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 electrodeV 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 specific example, the surfaces of these alloys are usually ground at 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 geonietrically irregular faces which introduce some diiiiculty in assembly of the rectiers. Thus, grinding` the alloy surface fiat and etching it appears to be the most feasible manner of producing the rectiers 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. Germanium 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 germaniumtin 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. 'I'his 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 segregated. At l'I atomic percent addition of tin, the entire melt was interlaced with tin-rich Veins which had metallic low resistance ohmic conductivity. y

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 reotiers 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 lessvthan 0.1 mil wasused as one electrode or Whisker, the other electrical contact usuallyv being made by soldering the alloy to a suitable conductor. However, tests have shown that the peak back voltages of rectillers 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 contactwith 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 rectiers using the alloys. These electrodes or whiskers may have contact with the surfaces of the alloys as formed upon solidication, 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 rectiers 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 mesh alumina (A1203). The abrasive used is not critical in that it has been found that other abrasives such as CrzOa, MgO, VazOa, SnOz, ZnO and 4-0 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 final 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 hydrouoric acid (48% reagent) 4 parts by volume distilled water 2 parts by volume concentrated nitric acid 200 milligrams Cu(NO3l2 to each 10 cc. of solution.

Such a solution will satisfactorily etch the surface ofthe 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 etche may be used effectively on the germanium alloys of our invention in addition to the etching above described.. Modified etching solutions and procedures are as follows:

A solution consisting approximately of 1 gram stannyl chloride in 50 cc. of H2O may be used as an electrolytic bath for etching the alloy surfaces. Immersing the alloy as the anode in this solution will result in satisfactory etching within about 11/2 minutes at about 21/2 volts applied.

An alternative modication of an electrolytic etching solution may comprise 5 parts concentrated HNOs and 50 parts H2O by volume. `Using the alloy as the anode for about 11/2 minutes at 1 to 2 volts will result in a satisfactory etch.

Reference may now be had to Figure 2 of the drawings illustrating the effect of etching of one of the alloys of our invention. The alloy selected to illustrate the effect of etching is identified as melt 24 P-OU136-.25Sn- This melt as appears frcm the aforesaid designation constitutes .25 atomic percent tin. The curveidentii'led by reference numeral i illustrates the electrical characteristic of the germanium-tin alloy above identified in which the surface was ground with 600;.lll2031butV not; etched. The .curve indicated by the reference numeral2 illustratesgthe elec#- trical characteristics whichwere 1 obtained` on a freshly broken. surface of analloyvof. the above compositionxbut which surface` has not been mannerY first described.

The curveindicated by the reference numeral 4 :illustrates electrical characteristics. of another point on the alloy. afteretchingas described'V inconnection with curve. 3, the curves 3^and lirep.-

resenting the besty and poorestperformances, respectively, of the particular germanium tin: alloy. above identified, after. etching. It `is to be.

ob'servedthat in this graph thevoltage scale in thefforward .direction isk thereexpanded. byv a. factor-'of 1,0, as .compared to the voltage scalev indicating. thehighgback voltage characteristics. ofthe alloys of .our invention. As indicated. the

currents are given..in-milliamperes.- Iii-.will be observed from an examination of Figurelz thatthe electrical characteristics of a rectifier using a broken surface exhibit high back voltagesv and forward conductances within the range of values obtained` when using; aground andetched surface. However, such broken surfaces are shiny-and geometricallyirregul'ar soiy that ithe Whisker tends to skid which' is undesirable-in assembling, permanent rectifier units. Frornyliigure 2 it is Yapparent that thethigh back voltage and high back resistance properties are inherentinthe alloysL and that the etching; is

eiective for restoring such properties after.-

grinding. Further, we have discovered that natural surfaces formed when solidifying. the alloys in Vacuum'will, if not :contaminated or otherwiseV affected by grinding, give -high back voltages and higlibacl; resistances when mounted andtested.

increaserin-the-back resistance can be effected byjapplyingpower overloa-ds -across'the contact. for-short intervals of time, each of length aboutl 1A hto l second or longer. The power treatment can -be effected with the-use of either alternating orf direct current.' Byk graduallyincreasing the voltage applied, and-hence the current-passed by thecontact during successive pulses, an optimum value can be found toA produce the maximum back resistance` for a-given contact. For direct cur.- rent. treatment in the forward direction such, op-

timum current .values rangefrom about 200 .toV y 800 .milliamperes For alternating power .treatment the optimum values of forward peak cur-- rent range from about 300 millialmperes to 1000 milliamperes. v 4 current treatment simply by connecting .the rectierlnseries with a current limiting` resistance. and'fth'e secondary of a transformer. Depending.

upon the size of this current limi-ting resistance, values of to 40 ohms have been used,lvoltage pulses ranging fromf? to Volts across the recti-v erandresistance serve to yield the maximum increase in back'resistanee..

Table IIIsh-o'ws thepermanent eie'cts .of such power treatment upon a few typical rectiiiers using alloysof'our invention and 'prepared as described." It'will'be seen from the tablethat..

the most significant effect of "the 'power treat! One can apply such alternating.

lof

10.? ment is.; the increase: in.: the` back resistance .as measured lat about :4;5: volts.

times@ the; values. measured before treatment. Relatively, minorzrincreases 1of 10. tov 20 per cent are Aeffectedron :the peak'ba'ck voltage. Forward currents. a-t one-.voltare :ingeneral decreased iby:

amounts ranging from'flO =to.50 percent..

' 'TABLE'III Ejecfs lof :power treatment [Values before power 'treatment are' followed in brackets by values after power treatment] Forward Peak'Back Current at Back Resist Alloy used in Rectifier.- .Voltagev one volt fgce (vom) (miui-y avg S amperesy. niego ms),

2411. 5() Sli" 75 :(105) t 0. .02; v 24L;50:SI1. 10C( (1&0) 11v (61.5). 30 95. (115) 13 25 `(2, 5) "(95)' 6 15 (8) 100 (120) 8 (S) 05 -(o. 8) A(115) 24 (10) 044 (7. 5) 90 (110) 20 (17) 48" (15)'y 150 (175) 40' (10) 2O (4) 90 (95) 10-(8) 20 (1) (120) 15A (10. 5) 13y (2) 80`(105) 18 (10) .10 (4) i (150) 4 (4) 40 (2) 90'A (95) 14 (8) 38V (2. 5) 40 (45) 30 (16) l 81 (3. 9) 80 (Q5) 16 (10) 1. (7. 5)

-Irt :has beendemonstrated.above that ythe high. back vo1tage,.high. back.- resistance, yand good fOr-- war-4d conductance properties 'disclosed are inherent in the. germanium alloys of our inven- ,tionf Modifications`fof'surfacel treatments or power.treatments.aszdescrbed above will, however, vary the magnitude of.y these proper-ties within.. certain general limits. ForY example, ona givenv alloy` surface, variations in surface treat# ment .andpower treatment maybe expected to vary the average peaklbackvoltage'by a factor of aboutzfthel average --forwardcurrent by a factor offab'outZ, andthe average backresistance by factors up to .50. It .willbenotedfth-atthe' backresi'stance is .the Aproperty -most lsensitive to variationsgin. treatment.,particularly toA power treat-v ment. .i

The following Table IV summarizesfon the.

basis. of .all melts made inw experimental work conducted under our. inventionpthe approximate germanium alloys consisting of the addition of a u single element.. a Y

TABLE -Iv Forward Currentr Peak Back Volte at onekvolt l Min. Av'e.Y Maxi Min. vev

This'resist-ance is increased by lfac-tors ranging from about: 10 to 50 (milliamperesl It will Vappear 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. For example, the nitrogen alloys can usually be expected to have 70 to 90 percent of back peak voltages over -60 volts. Values on the melts are more uniformly spread within the range of the limits given above. For the tin melts approximately 50% of the points on the surfaces' thereof will have voltages above 60 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 E. 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 semiconductor, and the Whisker for contacting the surface of the wafer being arranged and supported so that one end or 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 rectification 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 spirit and scope of our invention.

We claim: l

l. An electrical device comprising a semiconductor, a counter electrode having substantially point contactwith said semi-conductor and a second electrode having an area of contact with said semi-conductor which is large compared to that of the counter electrode, said semi-conductor consisting of germanium of the order of 99% purity in combination with at least one of the elements from the group consisting of magnesium, calcium, zinc, strontium, cadmium, and barium, said device having a peak back voltage in the range in excess of 10 volts and approaching the order of 200 volts.

2. An electrical device comprising an alloy formed of a mixture of germanium having a purity of the order of 99% and calcium in an amount of between 0.28 and 2.0 atomic percent, and a pair of electrode elements in contact with said formed alloy, one of said electrode elements having substantially point contact with said alloy and the second of said electrodes having an 3. An electrical device comprising an alloy i formed of a mixture of germanium having a purity of the order of 99% and strontium in an amount of between 0.5 and 1.0 atomic percent, and a pair of electrode elements in contact with said formed alloy, one of said electrode elements having substantially point contact with said a1- loy and the second of said electrodes having an area of contact which is large compared to that of the point contact electrode.

4. An electrical device comprising an alloy formed of a, mixture of germanium having a purity of the order of 99% and barium in an amount of between 0.4 and 0.5 atomic percent, and a pair of electrode elements in contact with said formed alloy, one of said electrode elements having substantially point contact with said alloy and the second of said electrodes having an area of Contact which is large compared to that of the point contact electrode.

5. The method of making an electrical device which comprises mixing germanium having la purity of the order of 99% with at least one of the elements from the class consisting of magnesium, calcium, zinc, strontium, cadmium, and barium, applying heat to the mixture to reduce the mixture to a fluid state, maintaining the heat for a time period suiiiciently long to permit mixing of the selected constituents, removing the heat to permit solidication or the mixture, cutting from the ingot formed upon mass solidication wafers to which contact electrodes may be applied, and applying contact electrodes to said wafers.

6. The method of claim 5, including the additional steps of grinding the severed wafers and then etching the ground surfaces to yprovide optimum contact points for said contacting electrode members.

'7. The method of claim 5, including, in addition, the step cf etching a surface of a wafer cut from the ingot before applying a contact electrode. y

8. The method of claim 5, including, in addition, the step of etching a surface of a wafer cut from the ingot in a solution made up of approximately 4 parts by volume of hydrofluori'c acid (48% reagent), 4 parts by volume of distilled water, 2 parts by volume of concentrated nitric acid, and 200 milligrams Cu(NO3)z to each 10 cc. of solution for a time period in the general range of between 1 and 2 minutes.

9. The method of claim 5, including securing one of saidelectrodes to one surface of a cut Wafer, locating a second substantially point contact electrodeupon a different surface of the cut wafer and in substantially point contact therewith, and then applying electric power between the electrodes and the Wafer.

10. The method of claim 9, including, inV addition, regulating the supplied current in the forwarddirectionthrough the cut wafer and limiting the current value to the range between 200 and 8.00 milliamperes applied in pulses of between 1A to l second in length.V Y p l1. IIfhe method of claim 10, including, in addition, the steps of connecting the formed device in series with a current limiting resistance anda secondary of a transformer of alternating electric currents controlling the peak current `in the forward direction to the order of between 300 and 1G00 milliamperes so that the voltage across the device 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 1A; and 1 second in time duration.

12. The method of claim 5, including electrolytically etching one of said wafers as an anode in a. solution in the proportions of approximately 1 gram stannyl chloride to 50 cc. water for about 11/2 minutes at about 21/2 Volts.

13. The method of claim 5, including electrolytically etching one of said wafers as an anode in a solution in the proportions of approximately 5 parts concentrated nitric acid to 50 parts water by Volume for about 11/2 minutes at about 1 to 2 Volts.

14. An electrical device comprising a semiconductor, a counter electrode 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 counter electrode, said semi-conductor consisting of germanium of the order of 99% purity in combination with at least one of the elements from the class consisting of magnesium, calcium, zinc, strontium, cadmium, and barium, said 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 device being in the order of between 10,000 ohms to several megohms at about 5 volts and the forward current being in the range of between 5 and 40 milliamperes at 1 volt in the low resistance direction of current ilow through the device.

15. An electrical device comprising a body of semi-conducting material consisting essentially of germanium of the order of 99% purity in combination with at least one element from the group consisting of magnesium, calcium, zinc, strontium, cadmium, and barium, and two electrodes in electrical contact with said body.

KARL LARK-HOROVITZ. RANDALL M. WHALEY.

REFERENCES CITED UNITED STATES PATENTS Name Date Woodyard Nov. 14, 1950 OTHER REFERENCES Merrit, Proc. Natl. Acad. Science, Vol. 11, 1925, pages 743-748.

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Claims (1)

1. AN ELECTRICAL DEVICE COMPRISING A SEMICONDUCTOR, A COUNTER ELECTRODE 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 COUNTER ELECTRODE, SAID SEMI-CONDUCTOR CONSISTING OF GERMANIUM OF THE ORDER OF 99% PURITY IN COMBINATION WITH AT LEAST ONE OF THE ELEMENTS FROM THE GROUP CONSISTING OF MAGNESIUM, CALCIUM, ZINC, STRONTIUM, CADMIUM, AND BARIUM, SAID DEVICE HAVING A PEAK BACK VOLTAGE IN THE RANGE IN EXCESS OF 10 VOLTS AND APPROACHING THE ORDER OF 200 VOLTS.

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