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This effect is known as "magnetoresist-ance.”

Ohio Semiconductors, Inc. has de-vcloped a device utilizing this cffcct and has tradcnamed it thc "Magneto-resistor." The type MS-41 utilizes a thin slice of indium antimonide. again because of thc high mobility of the charge carriers in this materiał. A re-sistance change of as much as 1 to 10 can be obtained with a change in field strength from ze^ro to 10,000 gauss. The change in rcsistance is propor-tional to the square of the magnetic field up to about 7000 gauss and is then directly proportional to field strength to over 20,000 gauss. A typi-cal characteristic curve is shown in Fig. 13.

This device has many possible appli-cations, including a contactless potenti-ometer, modulator chopper, amplifier, and regulator. The MS-41 h***'. a zero-field resistance of one ohm, but units having values ranging from 0.01 to 50 ohms are being developed.

Neutron Detection

One of the most unusual applications of semiconductor materials was reccnt-ly announced by Westinghou.se Electric Corp. Scientists at Westinghouse have developed a neutron detector madę of a tiny slice of germanium or Silicon no larger than the head of a pin. The slice is treated to form a p-n junction and a very thin layer of uranium is spread on the top surface.

Slow-speed neutrons strike this uranium layer and cause U-235 atoms to split apart just as they do in a nu-clear reactor. The high energv Products of this fission produce an electrical pulse at the p-n junction, and so can be counted. Fast neutrons do not produce fission and so are not counted, nor are gamma rays.

If desired. this neutron detector can be converted to count fast neutrons by replacing the uranium layer with a materiał rich in hydrogen, such as paraffin.

Accuratc mapping of both slow- and high-speed neutrons is a necessity in a nuclear reactor. Because of its very smali size, this detector can plot neutron fiux variations down to dimen-sional changes as smali as one twenty-fifth of an inch. Thus, this neutron detector can be a highly useful device whercver accurate neutron mapping is necessary. The size of thc detector is indicated in Fig. 14. where it is shown resting on a man’s thumbnail.

Conclusion

We have discussed here a few of the many possible applications of semiconductor materials. based on phe-nomena which have been explored in-tensivcly. Which of these will find wide usage is very hard to say at this time. but it is obvious that they are all of great interest. They are all products of the intensive research into the prop-erties of semiconductor materials which was sparked by the invention of the transistor at Bell Telephone Laboratories in 1948.

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