US2514879A - Alloys and rectifiers made thereof - Google Patents

Description

K. LARK-HoRovlTz Erm. 2,514,879

ALLOYS AND RECTIFIERS MADE THEREOF July 11, 1950 2 sneet's4s'heet 1 Fi1ed July 13, 1945 July'll, 1950 l K. LARK-HoRovlTz Erm.

LLOYS RECTIFIERS MADE THEREOF 2 Sheets-Sheet 2 Filed July 13, 1945 INVENTOR.

Karlar -150701/ Wma/a l W, www@ `at frequencies greater than about 1 to Patented July 1l, 1950 ALLoYs AND RECTIFIERS MADE THEREoF Karl Lark-Horovitz, La Fayette, and Randall M.

Whaley, West Lafayette, Ind., assignors to Purdue Research Foundation, La Fayette, Ind., a corporation of Indiana.

Application July 13, 1945, Serial No. 604,744

l2 Claims.

The present invention relates to an improvement in alloys of germanium, and more particularly to rectiers of electricity, which offer low resistance to current flow in one direction therethrough and high resistance to current 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 combined with germanium are not metals s 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 understood that the word alloy of germanium as used herein, means to include a union of two or more elements,` one of which is germanium, and the other or others being metals, non-metals, or gases, and the combination of which exhibits electrical properties such as are found in metals and semiconductors.

The known contact rectiflers, i. e., rectiers comprising suitable metal electrodes, and a semiconductor have at least one of the following disadvantages:

1. Inability to withstand in continuous use voltages in the' back or high resistance direction greater than aboutv 10 volts without permanent injury to the rectifier.

2. Inability to pass sufficient current in the forward direction for satisfactory operation of associated apparatus.

`3..Low back resistance prohibiting use of the cuits over about 100,000 ohms.y

Y `4.` Seriously decreased eiiiciency in rectifying 5 megacycles. Y i

5. Capacity ltoohigh to allow eflicient operation at frequenciesgreater than about 5 megacycles. Due to the aforesaid deficiencies of these known rectifier in high impedance circuits, that is, circontact rectiers, the art turned to widespread use of vacuum tube diodes for rectifying alternating currents. However, vacuum tube diodes, while overcoming certain of the aforementioned disadvantages of the known contact rectifiers, in turn have the following disadvantages:V

1. Inter-electrode capacities which are seriously objectionable at high frequencies.

2. Low forward direction conductance.

3. Requirement of power for heating a cathode.

4. Require a large amount of space as compared to a contact rectifier.

The germanium alloys of our present invention may be used as the semi-conductors for rectiers of the contact type, which, according to one embodiment ofour invention, possess the following general advantages over known contact rectifier-s:

1. yAbility to withstand continuous operating voltages greater than l0 volts in the back direction, and some of which are capable of with- 'age when ambient temperature increases from 23 C. to 75 C.

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

8. Do not require more `space than` about that Y needed for a common one-half watt carbon resistor.

40 The germanium alloys herein disclosed are all periodic table.

of the class of N-type semi-conductors, i. e., semi-conductors which when made into contact type rectifiers present a high resistance to current ilow across the rectifying contact when the semi-conductor is positive and the contacting metal electrode or Whisker is negative, and a lower resistance when the potential is reversed.

The variousr 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 voltage peak in the back or high resistance direction. This peak generally occurs Withina range greater than 10 volts and approaching the order of 200 volts. It will also appear that all of these rectirlers 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-ln the back or high resistance direction these rectiiiers have resistances ranging from the/order of 10,000 ohms to several megohms as measured at about 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 rectifers generally liewithin the range between 5 milliamperes and 40 milliam-` peres. 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 Aelements 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 of the periodic table;

Nitrogen, vanadium, columbium, tantaluxn, or bismuth of Column V of the periodic table;

Chromium or uranium of Column VI of the art with the manner of making alloysin accordance with our invention, land the utilization thereof as rectiiiers 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.

fIn the drawings:

Figure 1 shows the voltage-current characteristic curves of several rectiilers 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 isla graph illustrating the electrical characteristics of rectiilers using different types of surfaces lon one alloy of our invention.

Figure 3 is a sectional view of a rectifier, the

Isemi-conductor of which comprises anV alloy of our presentigivention.

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 Cobalt, nickel, or palladium of Column VIII nently injure the rectifying contact. It will be understood therefore that our present invention only relates to semi-conductors ofthe N-type which exhibit high back. voltage characteristics in excess of at least 10 volts, and does not concern all N-type semi-conductors consisting of an alloy of germanium, as for example, the group Y lastV referred to.

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

Now. is order to acquaint those skilled in the added to germanium to produce that alloy. No atomic percentage figures for the addition of nitrogen to germanium are given since it is diilcult to determine accurately the amount or number of nitrogen atoms alloyed with the germanium.

1n 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 vmade in accordance with the general procedure to be described later. The amount of the added element alloyed with germanium is set forth foreach melt in atomic per'- cent, i. e., the proportionate number of atoms in percent of the elements added to the total number of the atoms of germanium and Vadded 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 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 rangegiven. 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 vof the alloys disclosed at which the peak backvoltages, back resistances, or forward currents lie in the lower regions of the ranges given above forY thesevalues. Also ony the same surface of each alloy other points of contact may usually be found with electrical characteristics which lie4 toward theupper 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 rectication characteristics. 1

Additions to germanium TABLE I [In atomic per cent.)

Forward Current at l Peak Bgomm one volt D. C., Addition and percentages Muuampms Mln. Ave. Max Min. Ave. Max.

Bi: 1.0, .2), 1.25, .70, .28, .2), .31, 2.0, 2.5, 2.3, .023, .1), .80, .10, .40, .m1, .80, .80 15 50 l25 7 13 19 o: .50 20 30 35 10 15 20 Cb: .1), .43, .045.. 25 40 5 15 40 Cu: .60, 2.00, .42, .19, .34 .37, .40 15 40 75 1 5 40 Pb 3.0, .30, .50, .13, LIB, .35.-. n 25 70 135 l 15 25 Mg: 3.0, 3. 10 60 115 2 10 20 N 1.25, 10, .50, 1.0, 1.0, 1.0, 1.0, l 0 m 50 90 7 15 30 Ni: solidified in N i at pressures of 2, 18, 500, and 760, mm Hg 80 160 7 10 25 Pd: .50.- 30 65 110 5 15 25 Ag: .56, .50 40 80 7 10 20 sr: .5o. .50, .80, .80, .8o. .5o. .50, .50, 1.o, 1.o, 1.o, 1.o, .50, .50, .50, .50, .5o 25 75 15o 5 1o 25 Ta: .44 v 20 40 70 3 15 30 Sn: .50, .45, .82, .50, .50, .25, .05, .06, .10, .10, .75, .75,1.15, 2.80, .75, .78, .90, .90, .75, 2.2),

In Table II below there are set forth the melts in which two elements have been alloyed with germanium. The additions of these combinations of elements are also set forth in atomic percent as previously dened. It will be understood that the alloys set forth in this table are also to be included in the term lGroup A" above referred to for purposes of claiming our present v TABLE 1I M elts of more than one addition to germanzum [In atomic per cent.]

' Peak Back Voltage, Forward Current at A dditions and Volts one volt, Milliamperes Percentages Min. Ave. Max. Min. Ave. Max.

.zo Bi, .2n 25 5o s 15 .35 Cu, .7c s 4o 15o f 15 2o .21 Cu, .66 50 15 22 .21 Cu, .98 40 65 15 30 .80 Ca, .30 70 110 5 14 .80 Sr, .30 S 70 100 6 15 .50 Ni, .50 75 100 9 30 .50 Pd, .80 65 90 8 l5 .50 Pd, .80 50 95 5 12 .50 Ni, .10 Sr 50 95 8 15 .50 Ni, .30 Mg.- 50 75 12 20 .50 Ni, .30 C 45 75 10 20 .50 Ni, .50 Sr.., 40 50 9 12 .50 Ni, .50 SL... 25 35 10 15 .50 Ni, 1.00 Sr- 60 90 160 l0 15 .00 Ca, 1.00 Sr 10 30 50 13 20 0 Mg, .50 Srl0 30 45 10 20 .00 Ni, .50 Sr.. 65 100 7 10 .20 Sn, .32 Sr- 2) 100 165 6 13 .Z1 Sn, .32 Sr. 15 90 100 6 10 .00 Ni, .50 S11' 30 70 110 15 20 .00 Ni, .50 Sn 15 50 90 1 9 80 Ca, .40 C 35 75 140 2 7 80 Ca, .40 C l5 40 75 3 5 10 Sn, .40 Ca. 70 100 175 8 15 elements in either a high vacuum of the order of 10-5v mm. mercury at about 1000 C. or in an atmosphere of helium. Precaution should be taken to `prevent the accidental introduction of unknown and perhaps detrimental impurities into 1000 to 1050 C. Good results appear to be inthe melt from sources such as the crucible or boat in which the ingredients are disposed for melting, the furnace itself, or some material volatilized in the furnace. Alloying germanium with nitrogen may be effected by melting the germanium in an atmosphere of nitrogen which may be either purified nitrogen or nitrogen d irect from a commercial cylinder. The germanium is.

melted in nitrogen at pressures ranging from about 2 mm. to 760 mm. Hg at a temperature of dependent of pressure and melts prepared within the above range of pressures: were all satisfactory. v

The germanium successfully used for these alloys had purity approaching 100%, and electrical resistivity greater than about one ohm cm. The germanium which we have successfully alloyed with other elements to form the alloys listed in Tables I and II was prepared from GeOz obtained from the Eagle-Picher Lead Company of Joplin, Missouri. The oxide was reduced in anatmosphere 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 the germanium metal in the form of a gray-green powder which is then alloyed with another element or elements in the manner and proportions described.

The aforesaid melts Aof germanium and the l' added element or elements were held in the molten state long enough to allow mixing of the constituents, and it has been found that about 5 to 15 minutes is su'icient for this purpose. Usually ingredients to form melts of about ve to six grams each were used in proportions above set forth in detail. After the constituents had been allowed to mix, the melts` were allowed to solidify and cool which was accomplished either by immediately removing heat or by controlled cooling apparatus. In certain cases the uniformity of the melt is affected by the manner in which it is cooled. These variations will be discussed y later.

700 C. Six grams of pure germanium powder so obtained were then placed in a porcelain crucible together with small flakes oi pure tin amounting to 25 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 field of an induction furnace, and lowered in a vertical quartz tube which was then evacuated and maintained at a pressure of about 10 5 mm. mercury. the external coil of the induction furnace to melt the germanium and hold it molten for about minutes. The melt was then allowedto 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 elec trode 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 HNOz, 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 specific example, 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. surfaces present geometrically irregular faces which introduce some diiliculty in assembly of the rectifers. Thus, grinding the alloy surface flat 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. 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 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 h'ot 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 Power was then applied to Such broken the amount of bismuth actually remaining in the germanium during the melting cycle. A considerable fraction oi 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 rectiflers 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 rectiilers 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, Nl, 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 of tin were added in order to observe if.such

on the basis of requirements other than the peak back voltage on rectifiers using the alloys. These electrodes or whiskers may have contact with the ksurfaces of the alloys as formed upon solidiflcation, 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 mesh alumina (A1203). The abrasive used is not critical in that it has been found that other abrasives such as CrzAs, MgO, VaaOa, Sn02, ZnO and 4-0 paper are equally satisfactory. This vmay then be followed by a further grinding step 4 parts by volume hydrouoric acid (48% reagent) 4 parts by volume distilled water 2 parts by volume concentrated nitric acid 20o milligrams Cu(NOa)-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 vsince 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 of our invention in addition to the etching above described. Modied 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 sur- 9 faces. Immersing the alloy as the anodein this solution will result in satisfactory etching within about 11/2 minutes at about 21/2 volts applied.

An alternative modification of an' electrolytic' v etching solution may comprisey parts concentrated HNOs and 50 parts H2O by volume. Using the alloyas the anode for about 11/2 minutes at 1 to 2 volts will resultin 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 alloyselected to illustrate the effectof etching is identified as identied in which the surface was ground with 600 lA1203 but not etched. The curve indicated by the reference numeral 2 illustrates the electrical characteristics which were obtained on a freshly broken surface of an alloy of the above composition but which surface has not been etched. Curve member 3 illustrates the electrical characteristic of a surface ground withk 600 A1203 andv then etched in accordance with the manner first described.

The curve indicated by the reference numeral 4 illustrates electrical characteristics of another point on the alloy after etching as described in connection with curve 3, the curves 3 and 4 representing the best and poorest performances, respectively, of the particular germanium tin alloy above identified, after etching. It is to be observed that in this graph the voltage scale in the forward direction is there expanded by a factor of as compared to the voltage scale indicating the high back voltage characteristics of the alloys of our invention. As indicated, the currents are given in milliamperes.

1 inherent in the alloys and that the etching is effective for restoring such properties after grind; ing. Further, we have discovered that natural surfaces formed when solidifying the alloys in vacuum will. if not contaminated or otherwise affected Iby grinding, give high back voltages and ance serve to yield the treatment in the forward direction such optimum current values range from about 200 to 800 milliamperes. For alternatingv power treatment the optimum values of `forward peak current range from about 300 milliamperes to 1000 milliamperes. One can apply such alternating current treatment simplyjby connecting the rectifier in series with a current limiting resistance and the secondary of a transformer. this current limiting resistance, values of 10 to' 40 ohms have been used, voltage pulses ranging from 7 `to 60 volts across the rectifier and resistmaximum increase in back resistance.

Table III shows the'permanent eiects of such power treatment upon a few typical rectiers using alloys of our invention and prepared as described. AIt will be seen from the table that the most significant effect of the power treatment is the increase in the back resistance as measured at about 4.5 volts. This resistance is increased by factors ranging from about 10 to 50 times the values measured before treatment. Relatively minor high,backresistances'when mounted and tested 1n air.

lFor certain applications of these rectiers it is desirable that theyhave back resistances exceeding one megohm at` about 5 volts. Using the procedure described above will occasionally produce such high back resistances.l However, we have found that a substantial and permanent increase inthe back resistance can .be effected by applying power overloads across the contact, for short intervals oftime, leach of length about A tn 1 second or longer. The power treatment can be ef# lfected with the use of either alternating. or direct current. By gradually increasing the voltage applied,A and hence the current passed by the contact during successive pulses.' an optimum value can be found to produce the maximum backresistance for a given contact. For direct current increases of 10 to 20 percent are effected on the peak back voltage. Forward currents at one volt are in general decreased by amounts ranging from 10 to 50 percent. f

TABLE lII Effects of power treatment [Values before power treatment are followed in brackets by values after power treatment] V Forward Cur- Back Resist- Peak Back Alloy used in Rectifier voltage. ofltt fuglatts volts r l milliamperes megohms 75 (105) 9 (4. 5) 02 (3) 100 (140) 11 (6. 5) 30 (4) (115) 13 (7) .25 (2.5) (95) g e (c) .15 (s) (120) 8 (8) 05 8) 24 (10) 04 (7. 5) 90 (110) 20 (17) .48 (15) 150 (175) 40 (10) '.20 (4) 90 (95) i 10 (8) 20 (1) 100 (120) 15 (10. 5) .13 (2) 80 (105) 18 (10). .10 (4) (15G) 4 (4) .40 95 (115) 10 (6) 20 95 (105) l0 (6.4) .40 (7. 5) y 110 (120) 15 (10) .20 (3) It has been demonstrated above that the high back Voltage, high back resistance, and good forward conductance properties disclosed are innerent `in the germanium alloys of our invention. Modifications` of surface treatments or powerV treatments as described above will, howevenvary the magnitude of these properties within certain general limits. For example, on a given alloy surface, variations in surface treatment and power treatment may be expected to vary the average `peak back voltage by a factor of about y 2, the average forward current by a factor of basis of all melts made in experimental work con- Y ducted under` our inventiomthe approximate figures of the minimum, average, and maximum,

values of peak back voltage and forward current at one voltwhich might be expected on the ger- `manium alloysv consisting of the additionof a single element.l

`Depending upon thel size of plication in any desired circuitk for use in rectification of current.

" `Whilewe have disclosed what wel consider to be u the preferred .embodiments of our invention, it

willibe' understood that various modifications may be-madeftherein without departing from the Spirit TABLE IV Forward Current atv Peak Bg'tyoltge One Volt, milliam- Alloy peres,

Min. Ave. Max Min. Ave. Max.

25 75V 150 2 15 30 20 80 150 7 10 25 25 v 75 150 5 15 25 25 75A 150 5 l0 25 20 50 90 7 15 30 25 50 100 f `5 12 20 25 70 135 l 15 25 80 65 110 5 l5 25 10 50 100 '2 10 20 m 50 105 5 12 15 15 50 125 7 13 20 15 h 40 `3100 10 15 30 25 40 80 v 7 10 20 10 30 70 3 7 15 2o so as 1o 15 l zo m 40 70 3 15 30 15 40 75 1 5 40' 15 25 40 1 5 15 40 10 25 65 10 25 40 20 25 50 2 5 20 s 15 25 5 y i5 Az5 It will appear from the above tablel that the ranges of values for the better alloys appear to be quite similar. Dierences enter in the manner in whichthe 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 tin melts are more uniformly spread within the range ofthe 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.V `Following them, alloys of pure germanium with calcium,

strontium or nickel appear to be in order. It isl 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. s In Figure 3 of the drawings we have shown one typeof 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 9, 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. v The rectier contemplated by our invention may be of various forms, the only critical constructionalfeature being that the germanium alloy wafer comprising the'semi-conductor, and the Whisker for con- "wafer or semi-conductor and to the Whisker or metal electrode so that lthe device may have apthe -andscope'of our invention.

We claim: 1. An electrical device comprising a semi-conductor, a counter electrode having substantially point contact with said semi-conductor and a 5 vsecond electrode having any area of contact with said semi-conductor which is large compared to that of the counter electrode, said semi-conducr tor consisting of germanium of the order of 99% purity in combination with at least one of the elements from the class consisting oi' lead, tin, and titanium, and said device having a peak back voltage in the range in excess oi' 10 volts and approaching the order of 200 volts.

2. An electrical device comprising an alloy 15 formed of a mixture of'germanium having a pur- -ity of the order of 99% and tin in an amount of the order of .05 atomic percent, and a pair of electrode elements in contact with said formed alloy, one of said electrode `elements having sub- .stantially point contact with the said semi-conductor and the second of said electrodes havingan area of contact which is large compared to that of the'.A point contact electrode.

3.l The method of making an electrical device which comprises mixing germanium. having a purity ofthe order of 99% with at least one of the elements from the class consisting of lead, tin, and titanium, applying heat to the mixture to reduce the mixture to a fluid state, maintaining the heat for a time period sulciently long to permit mixing of the selected constituents, removing the heat to permit solidication of the mixture, cutting from the ingot formed upon mass solidiilcation wafers to which contact electrodes y be applied, and then applying said contact el'ectrodes to said wafers.

' 4. The method claimed in claim 3 comprising the additional steps oi grinding the severed wafer and then etching the ground surface to provide 40 optimum contact points for contacting electrode members.

5. The method claimedin claim 3 comprising in addition the step of etching a surface of the semi-conductor wafer which is cut from the ingot.

6. The method of claim 3 comprising the additional step of etching a surface of the semi-conductor wafer cut from the ingot in a solution in approximately the portions of 4 parts by volume of hydrofluoric acid (48% reagent). 4 parts by 50 volume distilled water, 2 parts by volume concentrated nitric acid and 200 milligrams Cu(NOa)z tov each 10 c. c. of solutionv for a time period in the general range between 1 and 2 minutes.

7. The method claimed in claim 3 comprising,

in addition, securing one of said contact electrodes to one surface of the cut wafer, locating a second substantially point contact electrode upon .a different surface of the cut wafer and in substantially point contact therewith, and then 50 applying electric power between the electrodes and the semi-conductor.

8. Themethod of claim 3.including electroy lytically etching the semi-conductor as an anode in a solution in the proportions oi' approximately 1 gram stannyl chloride to 50 c. c. of H2O for about 1 1/2 minutes at about 21/2 volts.

\ 9. The method of claim 3 including electrolytically etching the semi-conductor as an anode in a solution in the proportions of approximately 5 parts concentrated HNO: to 50 parts H2O by volxsme for about 11/2 minutes at about 1 to 2 vol 10. The method claimed in claim' 7 comprising, in addition, regulating the supplied current 1.10 the forward direction through the cut wafer and limiting the current value to the range being, in addition, the steps of connecting the 5 .resistance is of the order of between y7 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 V4 and 1 second in time duration.

12. An electrical device comprising a semi-con "ductor, 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 lead, tin, and titanium, to produce a device having a, peak KARL LARK-HOROVITZ. RANDALL M. WHALEY.

REFERENCES CITED Thefollowing references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,139,731 Boer Dec. 13, 1938 2,154,288 Scholz Apr. 11, 1939 2,162,613 Emmens ----4" June 13, 1939 l0 2,163,393 Brunke June 20, 1939 2,209,712 Brennan July 30, 1940 2,234,428 `Dean Mar. 11, 1941 2,237,802 Wittke Apr. 8, 1941 2,241,908 Herrmann May 13, 1941 15 2,361,680 Ehrhardt Oct. 31, 1944 2,375,181 Williams May 1, 1945l 2,375,355 Fahraeus May 8, 1945 FOREIGN PATENTS 2o Number Country Date 551,209 Great Britain Feb. 12, 1943 OTHER REFERENCES "On Contact Rectication by Metallic Germanium, an article by Ernest Merrit, published in'Proceedings Nationalk Academy of Sciences, vol. II, 1925, pages 743-748.

Journal of Physical Chemistry, vol. 33, 1929, pages 1085-4095.

Journal of Physical Chemistry, vol. 33, 1929, pages 1085 and 1092.

Journal of Physical Chemistry, vol. 34, 1930, pages 173-177. v

Journal of the American Chemical Society, vol. 52, 1930, pages 516-565,

5 chemical Abstracts, voi. a3, 1939, page 6694.

Chemical Abstracts, vol. 35, 1941, page 3152.

Thorpes Dictionary of Applied Chemistry, vol. 1, 4th edition, published by Iongmans. Green l: Co., page 330. n

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 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 LEAD, TIN, AND TITANIUM, AND 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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