1184 IEEE TRANSACTIONS ON ELECTRON DEVICES, OCTOBER 1976

compared to sodalite:I and sodalite:Cl and the fact that its op;ical absorption band lies in the part of the visible spectrum wherai the eye is the most sensitive. Since the luminescent sodaliLIxBr powder contains only a small amount of germanium, the position of the absorption band and the erase threshold are only s1ig::ltly affected. Therefore, in addition to being luminescent, this ma- terial is also a very suitable cathodochromic material.

Electron-beam coloration of these materials greatly reduces the luminescence observed under ultraviolet excitation. Si m e the peak wavelength of the F-center absorption band, -5501 A, occurs very near that of the emission band, 5250 %., much of the emission created within the colored material is reabsorlled. However, the measured reduction in emission intensity is la]-ger than that due merely to reabsorption [9], indicating that some quenching of the luminescence occurs as a result of the process by which the F-center is formed.

The exact mechanism which causes the luminescence observed in this study is not fully understood. However, several facts can be stated which must be considered in a model for this he- nomenon. First, although the emission is greatly enhanced by the substitution of germanium for silicon, germanium is not essential for the occurrence of the luminescence. Second, the luminescence appears to depend on either the creation of lattice vacancie,l or chemical reduction of ions present in the material since it is ob- served only after hydrogen annealing and since its intensity in- creases with both increasing annealing temperature and time up to the point where the sodalite structure collapses. Third, the emission is not due to the excitation of halogen ions since the same excitation and emission spectra are observed for genoa- nium-doped C1, I, and Br sodalite. Fourth, the decrease in lu- minescence intensity due to thermal mode coloration is gres: ter than expected on the basis of reabsorption alone, indicating that additional quenching occurs due to the formation of F-centlw. Further experiments are being conducted to provide additional evidence upon which a model can be based.

Experiments were conducted using 2” X 2” image screlms which were exposed to an electron beam in a demountable C12T system. The image screen is a sandwich structure consisting; of a glass substrate, a layer of evaporated aluminum, and the so- dalite powder. A Photo Research Brightness Spot Meter was wed to measure reflectance and emission. This instrument has a spectral response that is closely matched to that of the human eye. In high ambient light the image appears as dark purple in- formation on a white background while in low ambient, under ultraviolet excitation, the image is black-on-green. Due to reab- sorption and additional quenching of the luminescence whkh occurs upon coloration as mentioned above, the contrast ratio in low ambient can be much greater than the contrast ratio 5t en in high ambient light. An image screen of soda1ite:Br contain. ng three atomic percent Ge developed a reflective contrast ratic of 5:l in high ambient light when exposed to 150 &/cm2 usin 3: a 20-kV accelerating voltage. Under ultraviolet excitation in zoro ambient light, the contrast ratio was 201 with 14 fL being emit1,ed from the uncolored portion of the screen and 0.7 fL from .[.he colored area. The sample exhibited a saturation reflective con- trast ratio of 15:l in high ambient light and a contrast ratio greater than 120:l in zero ambient under ultraviolet exci;a- tion.

The above materials allow the construction of cathodochror lic CRT displays which not only have the properties of nornlal cathodochromic devices but also provide very-high-contrwt images in conditions of low illumination. Applications for su :h devices include displays in automobiles, airplane and helicopter cockpits, ships, and other night-vision uses [lo].

ACKNOWLEDGMENT The authors wish to thank Dr. Hans Jenssen of M.I.T. for k,is

assistance and the use of his laboratory in making luminescence measurements and Prof. D. J. Epstein for many helpful discus- sions.

REFERENCES

I. F. Chang and A. Onton, “Optical properties of photochromic sulfur-doped chlorosodalite,”J. Elect. Mat., vol. 2, no. 1, pp. 17-46, 1973. R. D. Kirk, “Role of sulfur in the luminescence and coloration of some aluminosilicates,”J. Electrochem. Soc., vol. 101, pp. 461-465, Sept. 1954. M. J. Taylor et al., “Colour centres in sodalites and their use in storage displays,” Radio and Electronic Engineer, vol. 40, pp. 17-25, July 1970. C. Z. van Doorn, D. J. Schipper, and P. T. Bolwijn, “Optical inves- tigation of cathodochromic sodalite,” J. Electrochem. Soc., vol. 119, pp. 85-91, Jan. 1972. S. K. Deb and J. B. Gallivan, “Photoluminescence of 0 2 - and S2- ions in synthetic sodalites,” J. Luminescence, vol. 5, pp. 348-360, 1972. C. Z. van Doorn and D. J. Schipper, “Luminescence of 0 2 - , Mn2+ and Fe3+ in sodalite,” Phys. Lett., vol. 34A, pp. 139-140, Feb. 1971. M. S. Perlmutter, L. T. Todd, Jr., and E. F. Farrell, “Lattice pa- rameters and chemical analysis of germanium substituted sodalite,” Mat. Res. Bull., vol. 9, pp. 65-70, 1974. L. T. Todd, Jr., E. F. Farrell, and A. Linz, “Process for preparing cathodochromic sodalite,” US Patent 3 932 592, Jan. 13,1976. L. T. Todd, Jr., “Investigation of the properties of cathodochromic sodalite and cathodochromic CRT display devices,” Ph.D. Thesis,

L. T. Todd, Jr., “Cathodochromic CRT display system for mobile M.I.T., Cambridge, MA, 1973.

communications,” in Proc. 1975 Carnahan Conference on Crime Countermeasures, pp. 181-184, University of Kentucky, May 1975.

Investigation of the Aging Processes of the p-n Junction Based on a Single Dislocation

S. KH. MIL’SHTEIN

Abstract-An investigation was made of the effects of aging on diodes based on 60” dislocations. The electrical properties of the dislocation p-n junctions showed good stability and were unaffected by the Cottrell impurity atmosphere. This property suggests that there are practical uses for semiconductor devices based on the principle of dislocations. A proposed assembly of the diode based on a single 60” dislocation is described.

It has been found that in a large group of point diodes the un- formed metal-semiconductor pressure contacts are very unstable [l]. Also, these contacts after formation have a big contact area. Furthermore, in both cases the diodes must still be tuned, Le., the sensitivity points of the crystal must be found. Nevertheless, after all this, not all parameters will approach desirable limits together. Only a small percentage of reliable devices are obtained after preaging.

In recent papers [2], [3] we reported the diode effect of a single 6 0 O dislocation in n-type silicon. This effect consists of strong rectification produced when the current flows through a tungsten microprobe which is located at the point of emergence of the dislocation. In n-type Si around the negative charge dislocation 60’ there apppeared a positive space-charge pipe, where the

Manuscript received March 1, 1976; revised May 11, 1976. The author is with The Racah Institute of Physics, The Hebrew Uni-

versity, Jerusalem, Israel.

CORRESPONDENCE 1185

-3 -2 -1 0 1 2 3

u ,volt Fig. 1. Current-voltage characteristics (CVC) of the diode, based on

a single dislocation (aging process). 1) CVC of the dislocation diode after 1 min. 2) CVC of the dislocation diode after 4 h. 3) CVC of the dislocation diode after 80 h. 4) CVC of the dislocation diode after 9000 h.

electrons were the minority carriers [4]. This cylinder p-n junc- tion was created without doping the host material or any elec- trical processing. The small height of the rectifying region, i.e., the small area of the p-n junction is caused by two factors: that the carriers spread out from a point contact and that there is a large pipe-area resistivity. The existence of this small area gives rise to good possibilities of working in the SHF range with such devices. In addition, the recovery of dislocation diodes after breakdown [3] greatly simplifies their protection against acci- dental overloads that often occur in SHF circuits.

In view of the above, it is important to determine the life du- ration of dislocation-type devices. I t is known [5] that p-n junc- tions and pressure contacts are subject to aging as a result of surface changes. The “dislocation detectors” are liable to undergo bulk aging associated witb the formation of Cottrell impurity atmospheres around the induced dislocations [6].

Since our previous measurements [2], [3] were carried out on freshly etched surfaces after 1 to 1.5 min, it was interesting to investigate the behavior of point-contact dislocation diodes with time. The aging of the diodes was therefore studied1 in the fol- lowing manner: Ohmic gold contacts were welded to n-type silicon crystal of p - 150 i7 cm. A tungsten microprobe of 0.5 to 1 pm in diameter was placed into the dislocation etch pit on the freshly etched surface of the sample (Fig. 2(a), (b), (c), and (d)) and the current-voltage characteristic (CVC) of the dislocation p-n junction was plotted (Fig. 1, curve 1). In order to study the aging process the tungsten needle was then bonded with a polymer or epoxy resin (Fig. 2(d) and (e)). The CVC of the junction was checked during polymerization to guard against any possible displacement of the needle by stresses arising while the com- pound was setting. One and a half to two hours after the bond had set, the needle was unclamped from the micromanipulator, and the CVC was plotted again. The results of aging are shown in Fig. 1. The forward branches of all curves coincide and are thus rep- resented by a single curve. The reverse branches of CVC 2,3, and 4, being virtually identical, are also drawn as a single (dashed) curve. CVC 2 was plotted after 4 h, and CVC 3 after 80 h.

Similar measurements were performed on about 10 samples. Fig. 1 indicates that reverse currents increase somewhat in the first few hours, apparently as a result of the formation of an oxide film, after which the CVC curves all follow the same pattern. The chemical activity of the bonding agents on silicon has not been tested: the resistance of the rectifying junctions to aging may, however, be attributed to the shielding action of oxide film, an

Institute of Solid State Physics of the Academy of Sciences of the Some of the experimental data were obtained by the author et the

USSR.

DISLOCATION ETCH P I T

a 1 KOo DISLOCATION

3

b

d

6

f 6

Fig. 2. The structural design of the semiconductor diode, based on the single 60’ dislocation. 1) n-type silicon wafer 1 X 1 X 0.3 mm. 2) Cold contact C#J 0.1 mm. 3) Kovar strip. 4) Tungsten needle. 5) Epoxy resin. 6) Lead. 7) Plastic capsule. 8) Silicon-organic coating.

effect that has been well demonstrated [7]-[8]. Lastly, curve 4 was plotted about a year (9000 h) after curves 1,2, and 3. During that time the diode experienced temperatures fluctuating from -5 to +3OoC and humidities up to 96-98 percent. The fact that curve 4 is virtually identical with curve 3 implies that the for- mation of an impurity atmosphere around the 60’ dislocation does not affect the diode action of the dislocation. The properties of dislocation-type rectifiers are accordingly not impaired by surface or bulk aging.

These findings suggest application of the given experimental technique for the manufacture of micromodular dislocation-type diodes without capsule sealing. Fig. 2 shows the design, approx- imate dimensions, and order of assembly of such a diode. A 0.5 X 0.5 X 0.1 mm Kovar strip is soldered to the gold base contact. A similar strip is connected to a tungsten contact 1.5 mm long, tapered at one end, and copper-plated and tinned at the other. After the microprobe is positioned in the dislocation etch pit and a control CVC curve has been plotted, the junction can be coated with some silicon organic material employed in the semicon- ductor industry, e.g., a “glimp” compound. As recommended [9], the tungsten contact can then be bonded with polymer resin. After drying, the device is encapsulated in plastic or ceramic.

Note again, that the influence, if any, of Cottrell atmospheres severely limits or makes absolutely impossible the application of dislocation devices in semiconductor electronics. However, the influence of Cottrell impurity atmospheres on the bulk aging of dislocation diodes has not been found. This enables construction of semiconductor devices based on the principle of disloca- tions.

ACKNOWLEDGMENT The author would like to thank Dr. Y. Brada for his constant

interest in this work.

REFERENCES [I] E. Spenke, Electronic Semiconductors. New York: McGraw-Hill,

[2] S. Kh. Mil’shtein and V. I. Nikitenko, JETP Let t . , vol. 13, p. 233, 1958, p. 71.

1971. [3] S: K h . Mil’shtein and V. I. Nikitenko, Souiet Phys. and Technic. of

Semicond. , vol. 6, no. 8, p. 1344, 1972.

Deuices, New York: Van Nostrand, 1965, p. 320.

379.

York: Van Nostrand, 1958, pp. 386, 391.

[a] H. Wolf, Semiconductors, New York: Wiley-Interscience, 1971, p.

[9] H. Bridgers, J. Scaff, and J. Shive, Transistor Technology, vol. 1, New