US2801376A - Alloys and rectifiers made thereof - Google Patents

Description

July 30, 1957 K. LARK-HoRovlTz ETAL 2,801,376

ALLOYS AND RECTIFIERS MAE THEREF 2 Sheets-Sheet l Original Filed July 15, 1945 July 30, 1957 K. LARKHoRovlTz ETAL 2,801,376

Alloys AND REmmERs MADE THEREOF 2 Sheets-Sheet 2 Original Filed July l5. 1945 e sts- @ya United States Patent O ALLOYS AND RECTIFIERS MADE THEREOF Karl Lark-Horovitz and Randall M. Whaley, Lafayette,

Ind., assignors to Purdue Research Foundation, Lafayette, Ind., a corporation of Indiana Original application July 13, 1945, Serial No. 604,744, now Patent No. 2,514,879, dated July 11, 1950. Di vided and this application December 29, 1949, Serial No. 135,748

This application is a division of application, Serial No. 604,744, tiled luly 13, 1945, and now Patent 2,514,879.

The present invention relates to an improvement in alloys of germanium, and more particularly to rectiers of electricity, which olfer low resistance to current tlow in one direction therethrough and high resistance to current ow 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 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 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, nonmetals, or gases, and the combination of which exhibits electrical properties such as are found in metals and semiconductors.

The known contact rectiers, i. e., rectitiers comprising suitable metal electrodes, and a semi-conductor have at least one of the following disadvantages:

l. Inability to withstand in continuous use voltages in the back or high resistance direction greater than about 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 rectifier in high impedance circuits, that is, circuits over about 100,000 ohms.

4. Seriously decreased eiliciency in rectifying at frequencies greater than about l to megacycles.

5. Capacity too high to allow efficient operation at frequencies greater than about 5 megacycles.

Due to the aforesaid deficiencies of these known contact rectiliers, 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 rectiers, in turn have the following disadvantages:

l. 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.v

2,801,376 Patented July 30, 1957 "ice which are capable of withstanding voltages in the back direction of an order approaching 200 volts.

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

3. High back resistances, at about 4 volts ranging from about 10,000 ohms to several megohms.

4. May be used with frequencies up to megacycles and will still rectify at 3,000 megacycles.

5. Provide rectilers of low capacity of about 0.5 micromicrofarad.

6. Less than 50 percent decrease in peak back voltage when ambient temperature increases from 23 C. to C.

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

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

The germanium alloys herein disclosed are all of the class of N-type semi-conductors, i. e., semi-conductors which when made into contact type rectiiiers present a high resistance to current tlow 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 various germanium alloys of our invention will be described and compared according to the properties they exhibit when made into contact type rectiers. Specic 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 within a range greater than 10 volts and approaching the order of 200 volts. It will also appear that all of these rectiers 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 rectiters generally lie within the range between 5 milliamperes and 40 milliarnperes. 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 milliamperes are sometimes deliberately passed momentarily in the forward direction to produce improvement in certain contact characteristics.

The N-type semiconductors 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 of the periodic table;

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

Chromium or uranium of column Vl 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, phosphorous, arsenic, or antimony with germanium, but in rectifiers using such semi-conductors it has been found that excessive currents pass at voltages greater than about 3 to 10 volts in the back direction which permanently injure the rectifying Contact. It will be understood therefore that our present invention only relates to semiconductors of the N-type which exhibit high back voltage characteristics in excess of at least volts, and does not concern all N-type semi-conductors consisting of an alloy of germanium, as for example, the group last referred to.

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

Now, in order to acquaint those skilled in the art with the manner of making alloys in accordance with our invention, and the utilization thereof as rectifiers 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 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 rectifiers using different types of surfaces on one alloy of our invention.

Figure 3 is a sectional view of a rectifier, the semiconductor 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 figures for the addition of nitrogen to germanium are given since it is dicult 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 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 rectictaion characteristics.

4 TABLE I Additions t0 germanium [In atomic percerm] Peak Brick Vriltagc Forward Current (Volts) at one volt D. C. Addition and percentages (Mllliamperes) Min. Avn. Max. Min. Ave. Max.

Ba; .40, .50 i5 50 125 7 13 i9 Bi: 1.0,.20, 1.25, .70, .28, .20, .31,

.40, .20, .80, .80 i5 50 125 7 13 i9 0d: .90, .30 20 50 105 8 i2 i5 Ca: 2.0, 1.35, .80, .50, .50, .28, .28,

.80, .80 25 75 150 5 15 25 Cr: .045, .50 5 15 25 5 15 25 C0: .50 20 30 35 10 15 20 Cb: .20, .43, .045 i5 25 40 5 15 40 Cu:.00,200,.42,.i0,.34,.37,.40 15 40 75 i 5 40 Pb;3.0,.30,.50, .i3,1.08,.35 25 70 135 i 15 25 Mg:3.0,3.0 i0 00 ii5 2 10 20 Ni: 1. 5, .10, .50, 1.0, 1.0, 1.0, 1.0,

1.0 20 50 90 7 15 30 N2: Solldled in Ni at pressures M2, i8, 600, 51151750, mmHg.. 20 80 100 7 i0 25 Pd:.50,.50 05 110 5 15 25 8585,50 25 40 80 7 10 20 Sr: .50, .50, .80, .80, .80, .50, .50,

. ,.0 25 75 150 5 10 25 Ta: .44 20 40 70 3 15 30 Sn; .50, .45, .82, .50, .50, .25, .05,

.40, .40, .40, .40, .40, .40, .40 25 75 150 2 15 30 Ti; .50, .50 10 30 70 a 7 15 U: .09, .09... 20 25 50 2 5 20 V: 1.0, 10 25 55 i0 25 40 Zn: .00, 25 50 100 5 i2 20 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 defined. lt will be understood that the alloys set forth in this table are also to be included 1n the term Group A above referred to for purposes of claiming our present invention. The

peak back voltages and the forward currents at one volt of rectiers made of these alloys are also set forth in this table.

TABLE II Melts of more than one addition to germanium Peak Back Forward Current` Additions and Percentages Voltage at one volt` (Volts) (Milliampervs) Min Ave Max. Miri. Ave. Mar

.3500, .70sn 25 40 150 i5 20 30 .2100, .65Sii 15 50 80 i5 22 50 neonata The germanium alloys of our invention may be prepared in all Ycases except for the germanium-nitrogen alloy, by melting pure germanium with the desired alloying element or combination of elements in either a high vacuum of the order of 10-5 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 the 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 direct 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 1000 to 10.50 C. Good results appear to be independent of pressure and melts prepared within the above range of pressures were all satisfactory.

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 GeOg obtained from the Eagle-Fieber Lead Company of Joplin, Missouri. The oxide was reduced in an atmosphere 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 of germanium and the 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 sufiicient for this purpose. Usually ingredients to form melts of about live 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 aifected by the manner in which it is cooled. These variations will be discussed later.

A specific melt in accordance with our invention was prepared as follows:

Pure GeOz was reduced in hydrogen at atmospheric pressure for about three hours at 650 to 700 C. Six grams of pure germanium powder so obtained were then placed in a porcelain crucible together with small flakes of 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 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 ol the power to the coil. Thereafter wafers were cut from the alloy, and were soldered with softsolder 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 HNOa, HF, Cu(NOs)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 wasused 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 ofthese alloys are usually ground Vliat 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 diiculty in assembly of the rectifiers. Thus, grinding the alloy surface flat 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 germaniumtin. 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 tinrich 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 conditons 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 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 diicult 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 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 l0 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 C203, M50;

VazOs, 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 mayV 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(Nos)z to each 10 cc. of solution Such a solution will satisfactorily etch the surface of the plates or slabs in about l 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 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 2V: volts applied.

An alternative modification of an electrolytic etching solution may comprise parts concentrated HNOa and S0 parts H2O by volume. Using the alloy as the anode for about 11/2 minutes at l to 2 bolts 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 24P-OUl36-.25Sn- This melt as appears from the aforesaid designation constitutes .25 atomic percent tin. The curve identified by reference numeral l illustrates the electrical characteristic of the germanium-tin alloy above identified in which the surface was ground with 600Al203 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 with 600Al2O3 and 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 particularly 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.

It will be observed from an examination of Figure 2 that the electrical characteristics of a rectifier using a broken surface exhibit high back voltages and forward conductances within the range of values obtained when using a ground and etched surface. However, such broken surfaces are shiny and geometrically irregular so that the Whisker tends to skid which is undesirable in assembling permanent rectifier units. From Figure 2 it is apparent that the high back voltage and high back resistance properties are inherent in the alloys and that the etching is effective 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 otherwise affected by grinding, give high back voltages and high back resistances when mounted and tested in air.

For certain applications of these rectifiers it is desirable that they have back resistances exceeding one megohm at about 5 volts. Using the procedure described above will occasionally produce such high back resistances. However, we have found that a substantial and permanent increase in the back resistance can be effected by applying power overloads across the contact, for short intervals of time, each of length about 1A to 1 second or longer. The power treatment can be effected with the use of either alternating or direct current. By gradually increasing the voltage applied, and hence the current passed by the contact during successive pulses, an optimum value can be found to produce the maximum back resistance for a given contact. For direct current treatment in the forward direction such optimum current values range from about 200 to 800 milliamperes. For alternating power treatment the optimum values of forward peak current range from about 300 milliamperes to 1000 milliamperes. One can apply such alternating current treatment simply by connecting the rectifier in series with a current limiting resistance and the secondary of a transformer. Depending upon the size of this current limiting resistance, values of l0 t0 40 ohms have been used, voltage pulses ranging from 7 to 60 volts across the rectifier and resistance serve to yield the maximum increase in back resistance.

Table III shows the permanent effects of such power treatment upon a few typical rectifiers using alloys of our invention and prepared as described. It 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 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.

TABLE III Effects of power treatment [Values before power treatment are followed in brackets by values nfter pow er treatin ont Forward Back Re- Pealr Back Current at sistance at Alloy Used in Rectifier Voltage one Volt 4.5 Volts (volts) (milli- (niegohms) amparos) 75 uns) 9 4.5) .02 (3) 11 6.5) .30 (4) 13 (T) .25 (2.5)

6 (fi) .15 (8) 8 (Si .05 (.8) 24(10) ,U4 (7. 5) 2f) (17) .48 (15) 40 (l0) .20 (4) 10 (8i .2D (l) l5 (10.5) .13 (2) 1s (i0) .10 (4) 4 (4) .40 (2) 1f] .20 (3) l0 (6.4) .40 (7. 5) 15 (l0) .20 (3) 14 t8) .38 (2.5) 30 (16) .81 (3. 9) 16 (1U) 1.0 (7. 5)

It has been demonstrated above that the high back voltage, high back resistance, and good forward conductance properties disclosed are inherent in the germanium alloys of our invention. Modifications of surface treatments or power treatments as described above will, however, vary 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 2, the average forward curent by a factor of about 2, and the average back resistance by factors up to 50. YIt will be noted that the back resistance is the property most sensitive to Vvariations in treatment, particularly to power treatment.

The following Table IV summarizes, on the basis of all melts rnade in experimental work conducted under our invention, the approximate gures 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 Yconsisting of the addition of a single element.

TABLE IV Peak Back Forward Current Voltage at One Volt Alloy (volts) (mllllamperes) Mln. Ave. Mar. Mtn. Ave. Max.

25 75 150 2 15 30 20 B0 160 'i' l0 25 25 75 150 5 l5 25 25 75 150 5 10 25 20 50 90 7 15 30 25 50 100 5 12 20 25 7l) 135 l 15 25 30 55 110 5 15 25 10 50 100 2 10 20 2U 50 105 5 12 l5 15 50 125 7 13 20 l5 40 100 l0 l5 30 25 40 80 7 l0 20 10 3l) 70 3 7 l5 2() 3D 35 10 l5 20 2t] 40 70 3 l5 30 l5 40 75 l 5 40 It will appear from the above table that the ranges of values for the better alloys appear to be quite similar. Diierences 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 tin melts are more uniformly spread within the range of the limits given above. For the tin melts approximately 50 percent 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 rectier 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 alloy above disclosed is mounted to have a low resistance non-rectifying contact with a metal electrode member 6. An electrode or Whisker 7 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 the members supporting the wafer 5 and electrode or Whisker 7 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 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 rectification of current.

While we have disclosed what we consider to be the preferred embodiments of our invention, it will be under# stood that various modifications may be made therein without departing from the spirit and scope of our invention.

We claim:

l. 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 chromium and uranium, said device having a peak back voltage in the range in excess of l0 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 chromium in an amount of between 0.045 and 0.50 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.

3. An electrical device comprising an alloy formed of a mixture of germanium having a purity of the order of 99% and uranium in an amount of 0.09 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.

4. The method of making an electrical device which comprises mixing germanium having a purity of the order of 99% with at least one of the elements from the class consisting of chromium and uranium, applying heat to the mixture to reduce the mixture to a uid state, maintaining the heat for a time period suciently long to permit mixing of the selected constituents, removing the heat to permit soliditication of the mixture, cutting from the ingot formed upon mass solidication wafers to which contact electrodes may be applied, applying contact electrodes to said wafers, securing one of said electrodes to one surface of a 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 applying electric power between the electrodes and the wafer by regulating the supplied current in the forward direction through the wafer and limiting the current value to the range between 200 and 800 milliamperes applied in pulses of between l/4 to 1 second in length.

5. The method of claim 4 including, 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 device and limiting resistance is of the order of between 7 and 60 volts and the limiting resistance is of the order of l0 to 40 ohms and regulating the period of application of the alternating current to intervals varying between 1A and l second in time duration.

6. 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 cornpared 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 chromium and uranium, 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 one volt in the low resistance direction of current ow through the device.

7. An electrical device comprising a body of semi-conducting germanium of the order of 99% purity in combination with at least one of the elements selected from the group consisting of chromium and uranium, and a pair of electrodes in electrical contact with said body, said chromium being present in an amount up to 0.5 atomic percent and said uranium being present in a amount up to 0.09 atomic percent.

8. An electrical device comprising a body of semiconducting material and a pair of electrodes in electrical contact with said body, said material comprising an alloy formed of a mixture of germanium having a purity of the order of 99% and chromium in an amount of between 0.045 and 0.50 atomic percent.

9. An electrical device comprising an alloy formed of a mixture of germanium having a purity of the order of 99% and uranium in an amount of 0.09 atomic percent, and a pair of electrode elements in electrical contact with said formed alloy.

10. A method of making an electrical device comprising alloying with a quantity of germanium semi-conducting material a small quantity of an impurity substance in order to impart to said germanium predetermined conductivity characteristics, cutting a wafer from the alloy thus formed, applying an electrode to a surface of said wafer, applying a substantially point contact electrode to another surface of said wafer, and applying an electric power overload between said point contact electrode and said Wafer for a short interval of time.

11. A method of making an electrical device comprising applying an electrode to a surface of a body of a semiconducting material comprising a germanium alloy, applying to another surface of said body a substantially point contact electrode, and applying electric power overloads between said point contact electrode and said body for short intervals of time.

12. The method of claim ll including, in addition, regulating the supplying current in the forward direction through the body and limiting the current value to the range between about 200 and 800 milliamperes applied in pulses of between about 1A second and 1 second in length.

13. The method of claim 12 including, in addition, controlling the peak current in the forward direction to between about 300 and 1000 milliamperes so that the voltage across the device is of the order of between 7 and 60 volts.

14. A method of treating an electrical device comprising a body of germanium semi-conducting material and a substantially point contact electrode in contact with a surface of said body, comprising applying an electric overload between said point contact electrode and said body for a short interval of time whereby to effect substantial improvement in the rectification properties of said device.

l5. An electrical device comprising a body of semiconducting material and a pair of electrodes in electrical contact with said body, said material comprising an alloy formed of a mixture of germanium having a purity of the order of 99% and chromium in an amount up to about 0.05 atomic percent.

16. A11 electrical device comprising a body of semiconducting material and a pair of electrodes in electrical contact with said body, said material comprising an alloy formed of a mixture of germanium having a purity of the order of 99% and uranium in an amount up to about 0.09 atomic percent.

17. The method of making an electrical device which comprises mixing germanium having a purity of the 0rder of 99% with at least one of the elements from the class consisting of chromium and uranium, applying heat to the mixture to reduce the mixture to a uid state, maintaining the heat for a time period suciently long to permit mixing of the selected constituents, removing the heat to permit solidication of the mixture, cutting from the ingot formed upon mass solidification wafers to which contact electrodes may be applied, etching a surface of said wafers in a solution made up of approximately 4 parts by volume of hydrofluoric acid (48% reagent), 4 parts by volume of distilled water, 2 parts by volume of concentrated nitric acid, and 200 milligrams Cu(NOs)2 to each l0 cc. of solution for a time period in the general range of between 1 and 2 minutes, and applying contact electrodes to said wafers.

18. The method of making an electrical device which comprises mixing germanium having a purity of the order of 99% with at least one of the elements from the class consisting of chromium and uranium, applying heat to the mixture to reduce the mixture to a fluid state, maintaining the heat for a time period sufficiently long to permit mixing of the selected constituents, removing the heat to permit solidification of the mixture, cutting from the ingot formed upon mass solidication wafers to which contact electrodes may be applied, 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 1%/2 minutes at about 2% volts, and applying contact electrodes to said wafer.

19. The method of making an electrical device which comprises mixing germanium having a purity of the order of 99% with at least one of the elements from the class consisting of chromium and uranium, applying heat to the mixture to reduce the mixture to a uid state, maintaining the heat for a time period sufficiently long to permit mixing of the selected constituents, removing the heat to permit solidication of the mixture, cutting from the ingot formed upon mass solidication wafers to which contact electrodes may be applied. electrolytically etching one of said wafers as an anode in a solution in the proportions of approximately S parts concentrated nitric acid to 50 parts water by volume for about 11/2 minutes at about l to 2 volts, and applying contact electrodes to said wafer.

References Cited in the tile of this patent UNITED STATES PATENTS

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 CHROMIUM AND URANIUM, 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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